/**
 *  date : 2020-11-30 22:08:30
 */

#define NDEBUG
#include <immintrin.h>
#define PROBLEM "http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=2945"
//
using namespace std;

// intrinstic
#include <immintrin.h>

// bits
#include <bits/stdc++.h>

// utility
namespace Nyaan {
using ll = long long;
using i64 = long long;
using u64 = unsigned long long;
using i128 = __int128_t;
using u128 = __uint128_t;

template <typename T>
using V = vector<T>;
template <typename T>
using VV = vector<vector<T>>;
using vi = vector<int>;
using vl = vector<long long>;
using vd = V<double>;
using vs = V<string>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<long long>>;

template <typename T, typename U>
struct P : pair<T, U> {
  template <typename... Args>
  P(Args... args) : pair<T, U>(args...) {}

  using pair<T, U>::first;
  using pair<T, U>::second;

  T &x() { return first; }
  const T &x() const { return first; }
  U &y() { return second; }
  const U &y() const { return second; }

  P &operator+=(const P &r) {
    first += r.first;
    second += r.second;
    return *this;
  }
  P &operator-=(const P &r) {
    first -= r.first;
    second -= r.second;
    return *this;
  }
  P &operator*=(const P &r) {
    first *= r.first;
    second *= r.second;
    return *this;
  }
  P operator+(const P &r) const { return P(*this) += r; }
  P operator-(const P &r) const { return P(*this) -= r; }
  P operator*(const P &r) const { return P(*this) *= r; }
};

using pl = P<ll, ll>;
using pi = P<int, int>;
using vp = V<pl>;

constexpr int inf = 1001001001;
constexpr long long infLL = 4004004004004004004LL;

template <typename T>
int sz(const T &t) {
  return t.size();
}
template <typename T, size_t N>
void mem(T (&a)[N], int c) {
  memset(a, c, sizeof(T) * N);
}

template <typename T, typename U>
inline bool amin(T &x, U y) {
  return (y < x) ? (x = y, true) : false;
}
template <typename T, typename U>
inline bool amax(T &x, U y) {
  return (x < y) ? (x = y, true) : false;
}

template <typename T>
int lb(const vector<T> &v, const T &a) {
  return lower_bound(begin(v), end(v), a) - begin(v);
}
template <typename T>
int ub(const vector<T> &v, const T &a) {
  return upper_bound(begin(v), end(v), a) - begin(v);
}

template <typename T>
int btw(T a, T x, T b) {
  return a <= x && x < b;
}

template <typename T, typename U>
T ceil(T a, U b) {
  return (a + b - 1) / b;
}

constexpr long long TEN(int n) {
  long long ret = 1, x = 10;
  for (; n; x *= x, n >>= 1) ret *= (n & 1 ? x : 1);
  return ret;
}

template <typename T, typename U>
pair<T, U> mkp(const T &t, const U &u) {
  return make_pair(t, u);
}

template <typename T>
vector<T> mkrui(const vector<T> &v, bool rev = false) {
  vector<T> ret(v.size() + 1);
  if (rev) {
    for (int i = int(v.size()) - 1; i >= 0; i--) ret[i] = v[i] + ret[i + 1];
  } else {
    for (int i = 0; i < int(v.size()); i++) ret[i + 1] = ret[i] + v[i];
  }
  return ret;
};

template <typename T>
vector<T> mkuni(const vector<T> &v) {
  vector<T> ret(v);
  sort(ret.begin(), ret.end());
  ret.erase(unique(ret.begin(), ret.end()), ret.end());
  return ret;
}

template <typename F>
vector<int> mkord(int N, F f) {
  vector<int> ord(N);
  iota(begin(ord), end(ord), 0);
  sort(begin(ord), end(ord), f);
  return ord;
}

template <typename T>
vector<T> reord(const vector<T> &v, const vector<T> &ord) {
  int N = v.size();
  vector<T> ret(N);
  for (int i = 0; i < N; i++) ret[i] = v[ord[i]];
  return ret;
};

template <typename T = int>
vector<T> mkiota(int N) {
  vector<T> ret(N);
  iota(begin(ret), end(ret), 0);
  return ret;
}

template <typename T>
vector<int> mkinv(vector<T> &v, int max_val = -1) {
  if (max_val < (int)v.size()) max_val = v.size() - 1;
  vector<int> inv(max_val + 1, -1);
  for (int i = 0; i < (int)v.size(); i++) inv[v[i]] = i;
  return inv;
}

}  // namespace Nyaan

// bit operation
namespace Nyaan {

__attribute__((target("popcnt"))) inline int popcnt(const u64 &a) {
  return _mm_popcnt_u64(a);
}

__attribute__((target("bmi"))) inline int botbit(const u64 &a) {
  return _tzcnt_u64(a);
}
__attribute__((target("bmi"))) inline int ctz(const u64 &a) {
  return _tzcnt_u64(a);
}

__attribute__((target("lzcnt"))) inline int topbit(const u64 &a) {
  return 63 - _lzcnt_u64(a);
}
__attribute__((target("lzcnt"))) inline int clz64(const u64 &a) {
  return _lzcnt_u64(a);
}

template <typename T>
inline int gbit(const T &a, int i) {
  return (a >> i) & 1;
}
template <typename T>
inline void sbit(T &a, int i, bool b) {
  a ^= (gbit(a, i) == b ? 0 : (T(b) << i));
}

constexpr long long PW(int n) { return 1LL << n; }

constexpr long long MSK(int n) { return (1LL << n) - 1; }

}  // namespace Nyaan

// inout
namespace Nyaan {

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  os << p.first << " " << p.second;
  return os;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
  is >> p.first >> p.second;
  return is;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  int s = (int)v.size();
  for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
  return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
  for (auto &x : v) is >> x;
  return is;
}

void in() {}
template <typename T, class... U>
void in(T &t, U &... u) {
  cin >> t;
  in(u...);
}

void out() { cout << "\n"; }
template <typename T, class... U, char sep = ' '>
void out(const T &t, const U &... u) {
  cout << t;
  if (sizeof...(u)) cout << sep;
  out(u...);
}

void outr() {}
template <typename T, class... U, char sep = ' '>
void outr(const T &t, const U &... u) {
  cout << t;
  outr(u...);
}

struct IoSetupNya {
  IoSetupNya() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(15);
    cerr << fixed << setprecision(7);
  }
} iosetupnya;

}  // namespace Nyaan

// debug
namespace DebugImpl {

void dump(const char& t) { cerr << t; }

void dump(const string& t) { cerr << t; }

template <typename T>
void dump(const T& t, enable_if_t<is_integral<T>::value>* = nullptr) {
  string res;
  if (t == Nyaan::inf) res = "inf";
  if (is_signed<T>::value)
    if (t == -Nyaan::inf) res = "-inf";
  if (sizeof(T) == 8) {
    if (t == Nyaan::infLL) res = "inf";
    if (is_signed<T>::value)
      if (t == -Nyaan::infLL) res = "-inf";
  }
  if (res.empty()) res = to_string(t);
  cerr << res;
}

template <typename T, typename U>
void dump(const pair<T, U>&);
template <typename T>
void dump(const pair<T*, int>&);

template <typename T>
void dump(const T& t,
          enable_if_t<!is_void<typename T::iterator>::value>* = nullptr) {
  cerr << "[ ";
  for (auto it = t.begin(); it != t.end();) {
    dump(*it);
    cerr << (++it == t.end() ? " ]" : ", ");
  }
}

template <typename T, typename U>
void dump(const pair<T, U>& t) {
  cerr << "( ";
  dump(t.first);
  cerr << ", ";
  dump(t.second);
  cerr << " )";
}

template <typename T>
void dump(const pair<T*, int>& t) {
  cerr << "[ ";
  for (int i = 0; i < t.second; i++) {
    dump(t.first[i]);
    cerr << (i == t.second - 1 ? " ]" : ", ");
  }
}

void trace() { cerr << endl; }
template <typename Head, typename... Tail>
void trace(Head&& head, Tail&&... tail) {
  cerr << " ";
  dump(head);
  if (sizeof...(tail) != 0) cerr << ",";
  trace(forward<Tail>(tail)...);
}

}  // namespace DebugImpl

using DebugImpl::trace;

#ifdef NyaanDebug
#define trc(...)                            \
  do {                                      \
    cerr << "## " << #__VA_ARGS__ << " = "; \
    DebugImpl::trace(__VA_ARGS__);          \
  } while (0)
#else
#define trc(...)
#endif

// macro
#define each(x, v) for (auto&& x : v)
#define all(v) (v).begin(), (v).end()
#define rep(i, N) for (long long i = 0; i < (long long)(N); i++)
#define repr(i, N) for (long long i = (long long)(N)-1; i >= 0; i--)
#define rep1(i, N) for (long long i = 1; i <= (long long)(N); i++)
#define repr1(i, N) for (long long i = (N); (long long)(i) > 0; i--)
#define reg(i, a, b) for (long long i = (a); i < (b); i++)
#define regr(i, a, b) for (long long i = (b)-1; i >= (a); i--)
#define repc(i, a, cond) for (long long i = (a); (cond); i++)

#define ini(...)   \
  int __VA_ARGS__; \
  in(__VA_ARGS__)
#define inl(...)         \
  long long __VA_ARGS__; \
  in(__VA_ARGS__)
#define ins(...)      \
  string __VA_ARGS__; \
  in(__VA_ARGS__)
#define inc(...)    \
  char __VA_ARGS__; \
  in(__VA_ARGS__)
#define in2(s, t)                           \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i]);                         \
  }
#define in3(s, t, u)                        \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i], u[i]);                   \
  }
#define in4(s, t, u, v)                     \
  for (int i = 0; i < (int)s.size(); i++) { \
    in(s[i], t[i], u[i], v[i]);             \
  }

#define die(...)             \
  do {                       \
    Nyaan::out(__VA_ARGS__); \
    return;                  \
  } while (0)

namespace Nyaan {
void solve();
}
int main() { Nyaan::solve(); }

//
using namespace std;

template <int DIM, typename Data_t = long long>
struct DimensionExpandedGraph {
  static_assert(is_signed<Data_t>::value, "Data_t must be signed.");
  using DG = DimensionExpandedGraph;

  struct A : array<int, DIM> {
    using array<int, DIM>::operator[];
#pragma GCC diagnostic ignored "-Wnarrowing"
    template <typename... Args>
    A(Args... args) : array<int, DIM>({args...}) {}
#pragma GCC diagnostic warning "-Wnarrowing"

    A &operator+=(const A &r) {
      for (int i = 0; i < DIM; i++) (*this)[i] += r[i];
      return *this;
    }
    A &operator-=(const A &r) {
      for (int i = 0; i < DIM; i++) (*this)[i] -= r[i];
      return *this;
    }
    A operator+(const A &r) { return (*this) += r; }
    A operator-(const A &r) { return (*this) -= r; }

    int id() const { return DG::id(*this); }
    friend int id(const A &a) { return DG::id(a); }

    bool ok() const { return DG::ok(*this); }
    friend bool ok(const A &a) { return DG::ok(a); }

    inline bool is_add() const { return (*this)[0] == ADD; }
    friend inline bool is_add(const A &a) { return a[0] == ADD; }

    vector<A> near() const {
      static vector<A> res;
      res.clear();
      if (is_add() == true) return res;
      for (int i = 0; i < DIM; i++) {
        A asc(*this), dec(*this);
        asc[i]++;
        dec[i]--;
        if (asc[i] != g_size[i]) res.push_back(asc);
        if (dec[i] != -1) res.push_back(dec);
      }
      return res;
    }
    friend vector<A> near(const A &a) { return a.near(); }
  };

  static int N, add_node;
  static A g_size, coeff;
  static constexpr int ADD = numeric_limits<int>::min();

  static int id(const A &a) {
    if (a[0] == ADD) return N + a[1];
    int ret = 0;
    for (int i = 0; i < DIM; i++) {
      ret += a[i] * coeff[i];
    }
    return ret;
  }
  template <typename... T>
  static int id(const T &... t) {
    return id(A{t...});
  }

  static bool ok(const A &a) {
    if (a[0] == ADD) {
      return 0 <= a[1] && a[1] < add_node;
    }
    for (int i = 0; i < DIM; i++)
      if (a[i] < 0 or g_size[i] <= a[i]) return false;
    return true;
  }
  template <typename... T>
  static bool ok(const T &... t) {
    return ok(A{t...});
  }

  static A ad(int n) { return A{DG::ADD, n}; };

  vector<char> grid;
  vector<Data_t> dat;

  explicit DimensionExpandedGraph() = default;
  template <typename... T>
  explicit DimensionExpandedGraph(const T &... t) {
    set(t...);
  }

  template <typename... T>
  void set(const T &... t) {
    N = 1;
    g_size = A{t...};
    coeff.fill(1);
    for (int i = 0; i < DIM; i++) {
      assert(g_size[i] != 0);
      for (int j = 0; j < i; j++) coeff[j] *= g_size[i];
      N *= g_size[i];
    }
    dat.resize(N + add_node, -1);
  }

  void add(int n) {
    add_node = n;
    dat.resize(N + add_node, -1);
  }

  void scan(istream &is = std::cin) {
    grid.reserve(N);
    int l = g_size[DIM - 1];
    for (int i = 0; i < N; i += l) {
      string s;
      is >> s;
      copy(begin(s), end(s), back_inserter(grid));
    }
  }

  friend istream &operator>>(istream &is, DG &g) {
    g.scan(is);
    return is;
  }

  vector<char> &get_grid() { return grid; }
  char &operator()(const A &a) { return grid[id(a)]; }
  template <typename... T>
  char &operator()(const T &... t) {
    return grid[id(t...)];
  }

  A find(const char &c) {
    A a{};
    fill(begin(a), end(a), 0);
    a[DIM - 1] = -1;
    while (true) {
      a[DIM - 1]++;
      for (int i = DIM - 1;; i--) {
        if (a[i] != g_size[i]) break;
        if (i == 0) return a;
        a[i] = 0;
        a[i - 1]++;
      }
      if ((*this)(a) == c) return a;
    }
  }

  template <typename F, typename Dist_t = Data_t>
  vector<Dist_t> bfs(F f, A s) {
    vector<Dist_t> dist(N + add_node, -1);
    if (!ok(s)) return dist;
    vector<A> Q;
    dist[id(s)] = 0;
    Q.push_back(s);
    while (!Q.empty()) {
      A c = Q.back();
      Q.pop_back();
      int dc = dist[id(c)];
      f(c, [&](A d) {
        if (!ok(d)) return;
        if (dist[id(d)] == -1) {
          dist[id(d)] = dc + 1;
          Q.push_back(d);
        }
      });
    }
    return dist;
  }

  template <typename F, typename Dist_t = Data_t>
  vector<Dist_t> bfs01(F f, A s) {
    vector<Dist_t> dist(N + add_node, -1);
    if (!ok(s)) return dist;
    deque<A> Q;
    dist[id(s)] = 0;
    Q.push_back(s);
    while (!Q.empty()) {
      A c = Q.front();
      Q.pop_front();
      int dc = dist[id(c)];
      f(c, [&](A d, Data_t w) {
        if (!ok(d)) return;
        if (dist[id(d)] == -1) {
          dist[id(d)] = dc + w;
          if (w == 0)
            Q.push_front(d);
          else
            Q.push_back(d);
        }
      });
    }
    return dist;
  }

  template <typename F, typename Dist_t = Data_t>
  static vector<Dist_t> dijkstra(F f, A s) {
    vector<Dist_t> dist(N, -1);
    using P = pair<Dist_t, A>;
    auto cmp = [](P &a, P &b) { return a.first > b.first; };
    priority_queue<P, vector<P>, decltype(cmp)> Q(cmp);
    assert(id(s) != -1);
    dist[id(s)] = 0;
    Q.emplace(0, s);
    while (!Q.empty()) {
      Dist_t dc;
      A c;
      tie(dc, c) = Q.top();
      Q.pop();
      if (dist[id(c)] < dc) continue;
      f(c, [&](A d, Dist_t w) {
        if (!ok(d)) return;
        if (dist[id(d)] == -1 || dist[id(d)] > dc + w) {
          dist[id(d)] = dc + w;
          Q.emplace(dc + w, d);
        }
      });
    }
    return dist;
  }

  // Union Find
  int find(A u) {
    return dat[id(u)] < 0 ? id(u) : dat[id(u)] = find(dat[id(u)]);
  }
  bool same(A u, A v) { return find(u) == find(v); }
  bool unite(A u, A v) {
    if ((u = find(u)) == (v = find(v))) return false;
    int iu = id(u), iv = id(v);
    if (dat[iu] > dat[iv]) swap(iu, iv);
    dat[iu] += dat[iv];
    dat[iv] = iu;
    return true;
  }
  Data_t size(A u) { return -dat[find(u)]; }
};

template <int DIM, typename Data_t>
int DimensionExpandedGraph<DIM, Data_t>::N = 0;
template <int DIM, typename Data_t>
int DimensionExpandedGraph<DIM, Data_t>::add_node = 0;
template <int DIM, typename Data_t>
typename DimensionExpandedGraph<DIM, Data_t>::A
    DimensionExpandedGraph<DIM, Data_t>::g_size;
template <int DIM, typename Data_t>
typename DimensionExpandedGraph<DIM, Data_t>::A
    DimensionExpandedGraph<DIM, Data_t>::coeff;

//
using namespace Nyaan;
void Nyaan::solve() {
  ini(n,m);
  DimensionExpandedGraph<3> g(n,n,2);

  vvi fee(n,vi(n));
  rep(i,m){
    ini(h,w,c);
    --h,--w;
    fee[h][w]=c;
  }

  auto d=g.dijkstra(
    [&](auto a,auto f) {
      each(nx,a.near()){
        if(nx[2]!=a[2])continue;
        f(nx, 1+fee[nx[0]][nx[1]]);
        if(a[2]==0){
          auto nx2 =nx;
          nx2[2]++;
          f(nx2, 1);
        }
      }
    }, {0,0,0}
  );

  out(min(d[g.id(n-1,n-1,0)],d[g.id(n-1,n-1,1)]));


}