#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;



int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int N,M; cin >> N >> M;
    if(N == 1){ cout << 0 << endl; return 0; }
    vector<vector<ll>> A(N, vector<ll>(M));
    rep(i,N)rep(j,M) cin >> A[i][j];

    vector<ll> dp = A[0];
    rep(i,N-1) {
        vector<ll> nt(M);
        vector<ll> L = dp, R = dp;
        for(int j = 0; j + 1 < M; j++)  L[j + 1] = min(L[j + 1], L[j]);
        for(int j = M - 1; j >= 1; j--) R[j - 1] = min(R[j - 1], R[j]);
        rep(j,M) {
            nt[j] = dp[j] + A[i + 1][j];
            if(0 <= j - 1) nt[j] = min(nt[j], L[j - 1] + A[i + 1][j] + A[i][j]);
            if(j + 1 <  M) nt[j] = min(nt[j], R[j + 1] + A[i + 1][j] + A[i][j]);
        }
        swap(dp, nt);
    }

    cout << *min_element(dp.begin(), dp.end()) << endl;
}