//#pragma GCC target("avx")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;

//local debug
#ifdef LOCAL
#include <debug_print.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif

#define overload4(a, b, c, d, e, ...) e

//alias
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using mint = modint998244353;
using Mint = modint1000000007;

//constants
constexpr const long long MOD = 998244353;
constexpr const long long MODM = 1000000007;
constexpr const int INF = 1e9;
constexpr const ll LINF = 1e18;

//rep(for-loop) macro
#define rep2(i, n) for(ll i = 0; i < n; i++)
#define rep3(i, k, n) for(ll i = k; i < n; i++)
#define rep4(i, k, n, a) for(ll i = k; i < n; i += a)
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2)(__VA_ARGS__)
#define rep1_2(i, n) for(ll i = 1; i <= n; i++)
#define rep1_3(i, k, n) for(ll i = k; i <= n; i++)
#define rep1_4(i, k, n, a) for(ll i = k; i <= n; i += a)
#define rep1(...) overload4(__VA_ARGS__, rep1_4, rep1_3, rep1_2)(__VA_ARGS__)
#define Rep2(i, n) for(ll i = n - 1; i >= 0; i--)
#define Rep3(i, k, n) for(ll i = n - 1; i >= k; i--)
#define Rep4(i, k, n, a) for(ll i = n - 1; i >= k; i -= a) 
#define Rep(...) overload4(__VA_ARGS__, Rep4, Rep3, Rep2)(__VA_ARGS__)
#define Rep1_2(i, n) for(ll i = n; i >= 1; i--)
#define Rep1_3(i, k, n) for(ll i = n; i >= k; i--)
#define Rep1_4(i, k, n, a) for(ll i = n; i >= k; i -= a) 
#define Rep1(...) overload4(__VA_ARGS__, Rep1_4, Rep1_3, Rep1_2)(__VA_ARGS__)
#define vfor(v, x) for(auto x : v)
#define mfor(map) for(auto &[key, value] : map)

//vector macro
#define vvecc(T, name, n, m) vector<vector<T>> name(n, vector<T>(m))
#define vvec(T, name, n) vector<vector<T>> name(n)
#define vvecs(T, name, n, m, s) vector<vector<T>> name(n, vector<T>(m, s))
#define all(x) begin(x), end(x)
#define LB(v, x) distance((v).begin(), lower_bound(all(v), (x)))
#define UB(v, x) distance((v).begin(), upper_bound(all(v), (x)))

//data structure macro
#define ef emplace_front
#define eb emplace_back
#define pf pop_front
#define pb pop_back
#define mp make_pair
#define fi first
#define se second
#define mt make_tuple
#define get(t, x) get<x - 1>(t)
#define lb lower_bound
#define ub upper_bound
template<class T> using pq = priority_queue<T>;
template<class T> using pqmin = priority_queue<T, vector<T>, greater<T>>;
template<class T, class U> using pqp = priority_queue<pair<T, U>>;
template<class T, class U> using pqpmin = priority_queue<pair<T, U>, vector<pair<T, U>>, greater<pair<T,U>>>;

//output
#define pl() cout << '\n'
template<class T> void print(const T& a) {cout << a;}
void printl(){}
template<class T> void printl(const T& t){print(t); pl();}
template<class Head, class... Tail> void printl(const Head& head, const Tail&... tail) {print(head); cout << " "; printl(tail...);}
template<class T> void fin(const T& t) {printl(t); exit(0);}
void Yes(bool a) {cout << (a ? "Yes" : "No") << '\n';}
template<class T, class U> void Out2(bool a, T yes, U no) {if(a) printl(yes); else printl(no);}

//functions
int ctoi(char c) {return c - '0';}
char to_char(int x) {return x + '0';}
template<class... T> constexpr auto Emin(T... a) {return min(initializer_list<common_type_t<T...>>{a...});}
template<class... T> constexpr auto Emax(T... a) {return max(initializer_list<common_type_t<T...>>{a...});}
template<class T, class U> bool chmax(T &a, const U &b) {if (a < b) { a = b; return true;} return false;}
template<class T, class U> bool chmin(T &a, const U &b) {if (a > b) { a = b; return true;} return false;}
template<class T, class U> ll Epow(T x, U y) {ll ans = 1; for(int i = 0; i < y; i++) ans *= x; return ans;}
template<class T, class U> ll Eceil(T x, U y) {return (ll)ceil((ld)x / (ld)y);}
template<class T, class U> ll Efloor(T x, U y) {return (ll)floor((ld)x / (ld)y);}
template<class T, class U> bool check_bit(T tar, U bit) {return ((tar & Epow(2, bit)) != 0);}

//---------------------------------------------------------------------------------------------------
int main() {

    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(10);

    int H, W;
    cin >> H >> W;
    vvecs(int, A, H + 1, W + 1, -1);
    rep1(i, 2, H - 1) {
        rep1(j, W) {
            cin >> A[i][j];
            if(A[i][j] == -1) A[i][j] = INF;
        }
    }

    vvecs(int, dp, H + 1, W + 1, INF);
    rep1(i, 2, H - 1) dp[i][0] = 0;
    
    rep(j, W) {
        rep1(i, 2, H - 1) {
            if(i - 1 > 1) chmin(dp[i - 1][j + 1], dp[i][j] + A[i - 1][j + 1]);
            chmin(dp[i][j + 1], dp[i][j] + A[i][j + 1]);
            if(i + 1 < H) chmin(dp[i + 1][j + 1], dp[i][j] + A[i + 1][j + 1]);
        }
    } 

    debug(dp);

    int ans = INF;
    rep1(i, 2, H - 1) chmin(ans, dp[i][W]);
    Out2(ans == INF, -1, ans);
}