#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
int n,m,top,ans = 2e9,lg[N],h[N],st[N],L[N],R[N];
char ch[N];
vector <int> a[N];
int f(int len,int l,int r)
{
	if(l > r) swap(l,r);
	int c1,c2,n = len + l + r;
	c1 = lg[(len + l - 1) / len] + 1;
	len = (len << c1) - (len - l % len) % len;
	c2 = lg[(n - 1) / len] + 1;
	return c1 + c2;
}
int main()
{
	scanf("%d%d",&n,&m);
	for(int i = 1;i <= n;i++)
	{
		scanf("%s",ch + 1);
		a[i].resize(m + 1);
		for(int j = 1;j <= m;j++) a[i][j] = ch[j] - '0';
	}
	lg[0] = -1;
	for(int i = 2;i <= max(n,m);i++) lg[i] = lg[i >> 1] + 1;
	for(int i = 1;i <= n;i++)
	{
		for(int j = 1;j <= m;j++) h[j] = a[i][j] * (h[j] + 1);
		st[top = 0] = 0;
		for(int j = 1;j <= m;j++)
		{
			while(top && h[st[top]] >= h[j]) top--;
			L[j] = st[top],st[++top] = j;
		}
		st[top = 0] = m + 1;
		for(int j = m;j >= 1;j--)
		{
			while(top && h[st[top]] >= h[j]) top--;
			R[j] = st[top],st[++top] = j;
		}
		for(int j = 1;j <= m;j++)
			if(h[j]) ans = min(ans,f(h[j],i - h[j],n - i) + f(R[j] - L[j] - 1,L[j],m - R[j] + 1));
	}
	printf("%d\n",ans);
	return 0;
}