// what is matter? never mind. 
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,sse4,popcnt,abm,mmx,avx,avx2")
#include<bits/stdc++.h>
#define For(i,a,b) for(int i=(a);i<=(b);++i)
#define Rep(i,a,b) for(int i=(a);i>=(b);--i)
#define ll long long
#define ull unsigned long long
//#define int long long
#define SZ(x) ((int)((x).size()))
#define ALL(x) (x).begin(),(x).end()
using namespace std;
inline int read()
{
	char c=getchar();int x=0;bool f=0;
	for(;!isdigit(c);c=getchar())f^=!(c^45);
	for(;isdigit(c);c=getchar())x=(x<<1)+(x<<3)+(c^48);
	return f?-x:x;
}

#define fi first
#define se second
#define pb push_back
#define mkp make_pair
typedef pair<int,int>pii;
typedef vector<int>vi;

#define maxn 2000005
#define inf 0x3f3f3f3f

int n,m;
string s[maxn];
int h[maxn];
int st[maxn],tp;
int L[maxn],R[maxn];

int lg[maxn];

int calc(int len,int d1,int d2){
	if(d1>d2) swap(d1,d2);
//	cout<<"calc "<<len<<" "<<d1<<' '<<d2<<"\n";
	int n=len+d1+d2;
	if(d1%len==0) return lg[(n-1)/len+1];
	int w=(d1-1)/len+1,x=len-d1%len;
	return min(lg[(d2-1)/len+2]+1,lg[w+1]+lg[(n-1)/((len<<lg[w+1])-x)+1]);
}

signed main()
{
	n=read(),m=read();
	For(i,2,max(n,m)) while((1<<lg[i])<i)++lg[i];
	For(i,0,n-1)cin>>s[i];
	int res=4e18;
	For(i,0,n-1){
		For(j,0,m-1){
			if(s[i][j]=='0')h[j]=0;
			else h[j]++;
		}
		st[tp=0]=-1;
		For(j,0,m-1){
			while(tp && h[st[tp]]>=h[j])--tp;
			L[j]=st[tp],st[++tp]=j;
		}
		st[tp=0]=m;
		Rep(j,m-1,0){
			while(tp && h[st[tp]]>=h[j])--tp;
			R[j]=st[tp],st[++tp]=j;
		}
		For(j,0,m-1) if(h[j]) {
		//	cout<<"h,l,r "<<j<<" "<<h[j]<<' '<<L[j]<<" "<<R[j]<<"\n";
			res=min(res,calc(R[j]-L[j]-1,L[j]+1,m-R[j])+calc(h[j],i-h[j]+1,n-1-i));
		}
	}
	cout<<res;
	return 0;
}

/*

*/