// clang-format off
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
template<class T> using V = vector<T>;
using VI = V<int>;
using VL = V<ll>;
using VS = V<string>;
template<class T> using PQ = priority_queue<T, V<T>, greater<T>>;
using G = V<VI>;
template<class T> using WG = V<V<pair<int, T>>>;
#define overload4(_1,_2,_3,_4,name,...) name
#define rep1(n) for(ll i=0;i<(n);++i)
#define rep2(i,n) for(ll i=0;i<(n);++i)
#define rep3(i,a,b) for(ll i=(a);i<(b);++i)
#define rep4(i,a,b,c) for(ll i=(a);i<(b);i+=(c))
#define rep(...) overload4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define rrep1(n) for(ll i=n;i>0;--i)
#define rrep2(i,n) for(ll i=n;i>0;--i)
#define rrep3(i,a,b) for(ll i=b;i>a;--i)
#define rrep4(i,a,b,c) for(ll i=(a)+((b)-(a)-1)/(c)*(c);i>=(a);i-=c)
#define rrep(...) overload4(__VA_ARGS__,rrep4,rrep3,rrep2,rrep1)(__VA_ARGS__)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define inside(h,w,y,x) (unsigned(y)<h&&unsigned(x)<w)
#ifdef _DEBUG
#define line cout << "-----------------------------\n"
#define debug(...) print(__VA_ARGS__)
#else
#define line
#define debug
#endif
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 61;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr int dy[]{ -1,0,1,0 }, dx[]{ 0,1,0,-1 };
template<class T> inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; }return false; }
template<class T> inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T> inline istream& operator>>(istream& is, V<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T, class U> inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T> inline V<T> vec(size_t a) { return V<T>(a); }
template<class T> inline V<T> defvec(T def, size_t a) { return V<T>(a, def); }
template<class T, class... Ts> inline auto vec(size_t a, Ts... ts) { return V<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts> inline auto defvec(T def, size_t a, Ts... ts) { return V<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }
template<class T> inline void print(const T& a) { cout << a << "\n"; }
template<class T, class... Ts> inline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); }
template<class T> inline void print(const V<T>& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << (i == v.size() - 1 ? "\n" : " "); }
template<class T> inline void print(const V<V<T>>& v) { for (auto& a : v)print(a); }
template<class T> inline constexpr const T cum(const V<T>& a, int l, int r) { return 0 <= l && l <= r && r < a.size() ? a[r] - (l == 0 ? 0 : a[l - 1]) : 0; }//[l,r]
template<class T> inline constexpr const auto min(const T& v) { return *min_element(all(v)); }
template<class T> inline constexpr const auto max(const T& v) { return *max_element(all(v)); }
template<class T> inline V<T>& operator++(V<T>& v) { for (T& a : v)++a; return v; }
template<class T> inline V<T>& operator--(V<T>& v) { for (T& a : v)--a; return v; }
// clang-format on

int main() {
    init();

    int n, m;
    cin >> n >> m;
    auto a = vec<int>(n, m);
    cin >> a;
    auto dp = defvec(LLINF, n, m, 2);
    PQ<tuple<ll, int, int, int>> pq;
    rep(j, m) {
        dp[0][j][0] = 0;
        pq.emplace(0, 0, j, 0);
    }
    while (!pq.empty()) {
        auto [d, i, j, payed] = pq.top();
        pq.pop();
        if (dp[i][j][payed] < d) continue;
        if (i == n - 1) continue;
        if (payed) {
            if (chmin(dp[i][j][payed ^ 1], dp[i][j][payed])) {
                pq.emplace(dp[i][j][payed ^ 1], i, j, payed ^ 1);
            }
            if (chmin(dp[i + 1][j][payed], dp[i][j][payed] + a[i + 1][j])) {
                pq.emplace(dp[i + 1][j][payed], i + 1, j, payed);
            }
        }
        else {
            if (chmin(dp[i][j][payed ^ 1], dp[i][j][payed] + a[i][j])) {
                pq.emplace(dp[i][j][payed ^ 1], i, j, payed ^ 1);
            }
            if (j + 1 < m && chmin(dp[i][j + 1][payed], dp[i][j][payed])) {
                pq.emplace(dp[i][j + 1][payed], i, j + 1, payed);
            }
            if (j - 1 >= 0 && chmin(dp[i][j - 1][payed], dp[i][j][payed])) {
                pq.emplace(dp[i][j - 1][payed], i, j - 1, payed);
            }
        }
    }
    ll ans = LLINF;
    rep(j, m) rep(payed, 2) chmin(ans, dp[n - 1][j][payed]);
    print(ans);

    return 0;
}