/*
    Task    : _example
    Author  : Phumipat C. [MAGCARI]
    Language: C++
    Created : 09 November 2022 [18:57]
*/
#include<bits/stdc++.h>
using namespace std;
int a[510][510],dp[510][510];
int main(){
    int n,m;
    scanf("%d %d",&n,&m);
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
            scanf("%d",&a[i][j]);
    for(int i=1;i<=n;i++){
        for(int j=1;j<=m;j++){
            if(j>1 && j<m)
                dp[i%2][j] = min({dp[(i-1)%2][j-1],dp[(i-1)%2][j],dp[(i-1)%2][j+1]}) + a[i][j];
            else if(j == 1)
                dp[i%2][j] = min(dp[(i-1)%2][j],dp[(i-1)%2][j+1]) + a[i][j];
            else if(j == m)
                dp[i][j] = min(dp[(i-1)%2][j-1],dp[(i-1)%2][j]) + a[i][j];
        }
    }
    int mn = 1e9;
    for(int j=1;j<=m;j++)
        mn = min(mn,dp[n%2][j]);
    printf("%d\n",mn);
    return 0;
}