#include <bits/stdc++.h>
using namespace std;
int n,m,dp[51][51][51][51],r[51][51];
int f(int i, int j, int k, int l){
if (i==k&&j==l)
return 0;
if (dp[i][j][k][l])
return dp[i][j][k][l];
dp[i][j][k][l]=1e9;
for (int m=i;m<k;m++)
dp[i][j][k][l]=min(dp[i][j][k][l],f(i,j,m,l)+f(m+1,j,k,l));
for (int m=j;m<l;m++)
dp[i][j][k][l]=min(dp[i][j][k][l],f(i,j,k,m)+f(i,m+1,k,l));
dp[i][j][k][l]+=r[k][l]-r[i-1][l]-r[k][j-1]+r[i-1][j-1];
return dp[i][j][k][l];
}
int main(){
ios_base::sync_with_stdio(NULL);cin.tie(nullptr);
cin >> n >> m;
for (int i=1;i<=n;i++)
for (int j=1;j<=m;j++){
cin >> r[i][j];
r[i][j]+=r[i][j-1]+r[i-1][j]-r[i-1][j-1];
}
cout << f(1,1,n,m);
}
