#include <bits/stdc++.h>
using namespace std;
const int N = 3, M = 1e6 + 1;
const int N1 = 151, M1 = 5001;
int pre[N][M], pre1[N1][M1];
int main()
{
ios::sync_with_stdio(0);
cin.tie(NULL), cout.tie(NULL);
int n,m,cnt=0,a;
cin>>n>>m;
if (n>2)
{
for (int i=1;i<=n;i++)
{
string s;
cin>>s;
int su=0;
for (int j=1;j<=m;j++)
a=s[j-1]-'0', su+=1-a*2, cnt+=a, pre1[i][j]=pre1[i-1][j]+su;
}
int ans=n*m;
for (int i=0;i<n;i++)
for (int i1=i+1;i1<=n;i1++)
{
int mn=0;
for (int j=1;j<=m;j++)
ans=min(ans,pre1[i1][j]-pre1[i][j]+mn+cnt), mn=min(mn,pre1[i][j]-pre1[i1][j]);
}
cout<<ans<<endl;
return 0;
}
for (int i=1;i<=n;i++)
{
string s;
cin>>s;
int su=0;
for (int j=1;j<=m;j++)
a=s[j-1]-'0', su+=1-a*2, cnt+=a, pre[i][j]=pre[i-1][j]+su;
}
int ans=n*m;
for (int i=0;i<n;i++)
for (int i1=i+1;i1<=n;i1++)
{
int mn=0;
for (int j=1;j<=m;j++)
ans=min(ans,pre[i1][j]-pre[i][j]+mn+cnt), mn=min(mn,pre[i][j]-pre[i1][j]);
}
cout<<ans<<endl;
return 0;
}
