#include<bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i = 0; i < n; i++)
#define rrep(i,n) for (int i = (n) - 1; i >= 0; i--)

int n,m;
ll A[1010][1010],dp[1010][1010],L[1010],R[1010];
int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    cin>>n>>m;
    rep(i,n)rep(j,m)cin>>A[i][j];
    if(n==1){
        cout<<0<<"\n";
        return 0;
    }
    rep(i,n)rep(j,m)dp[i][j]=1LL<<60;
    rep(i,m)dp[0][i]=A[0][i];
    rep(i,n-1){
        L[0]=1LL<<60;;
        rep(j,m-1){
            L[j+1]=min(L[j],dp[i][j]);
        }
        R[m-1]=1LL<<60;
        rrep(j,m-1){
            R[j]=min(R[j+1],dp[i][j+1]);
        }
        rep(j,m){
            dp[i+1][j]=min(dp[i][j]+A[i+1][j],min(L[j],R[j])+A[i][j]+A[i+1][j]);
        }
    }
    ll ans=1LL<<60;
    rep(i,m)ans=min(ans,dp[n-1][i]);
    cout<<ans<<"\n";
}