#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define pb push_back
#define int long long
#define repp(i,x,n) for(int i=x;i<=n;i++)
#define rep(i,x,n) for(int i=x;i>=n;i--)
#define cy cout<<"YES"<<endl
#define cn cout<<"NO"<<endl
#define ca cout<<"Alice"<<endl
#define r0 return 0
#define fi first
#define se second
#define liow ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define jelek cout<<"jelek"<<endl
#define pii pair<int,int>
#define all(v) v.begin(),v.end()
#define pi pair<pair<int,int>,pair<int,int>>
#define p3 pair<int,pair<int,int>>
#define p2
#define tp tuple<int,int,int>
#define fl fflush(stdout)
#define ld long double
#define p5 pair<int,pair<pair<int,int>,pair<int,int>>>
#pragma GCC optimize ("O2")
#pragma GCC optimize ("unroll-loops")
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;
typedef tree<pair<int,int>, null_type, less<pair<int,int>>, rb_tree_tag, tree_order_statistics_node_update> ordered_multiset;
typedef long long bryson;
const int mod=1e9+7;
const int SQMAX=635,INF=1e18;
//const int mod=998244353;
//const int MOD=1e6+3;
mt19937_64 rng((unsigned int) chrono::steady_clock::now().time_since_epoch().count());
pii dr[8]={{-1,0},{-1,1},{0,1},{1,1},{1,0},{1,-1},{0,-1},{-1,-1}};
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
int dxx[4]={1,1,-1,-1};
int dyy[4]={1,-1,-1,1};
int mul(int x,int y){return (x%mod*y%mod)%mod;}
int expo(int b,int e){
if(e==0) return 1;
int tmp=expo(b,e/2);
if(e%2) return mul(tmp,mul(tmp,b));
else return mul(tmp,tmp);
}
signed main(){
ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
int n,m;cin>>n>>m;
int a[n+2][m+2];
memset(a,0,sizeof a);
int satu=0;
repp(i,1,n){
repp(j,1,m){
char x;cin>>x;
if(x=='1') a[i][j]=1;
else a[i][j]=-1;
if(a[i][j]==1) satu++;
if(i>1) a[i][j]+=a[i-1][j];
}
}
int maks=0,nw=0,banyak=0,brp=0;
repp(l,1,n){
repp(i,l,n){
repp(j,1,m){
nw+=a[i][j]-a[i-l][j];
brp+=l;
if(nw<0){
nw=0,brp=0;
}
if(maks<nw){
maks=nw;
banyak=brp;
}
if(j==m) brp=nw=0;
}
}
}
int ans=satu-maks;
// cout<<satu<<" "<<banyak<<" "<<maks<<endl;
cout<<ans<<endl;
}
