#include <bits/stdc++.h>
#define ff first
#define ss second
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

void get(int l, int r, vector<pii> &V) {
    V.push_back({l, r});
    if (l == r) return;

    int m = (l + r) / 2;
    if ((r - l + 1) % 2 == 0) {
        get(l, m, V);
        get(m + 1, r, V);
    }
    else {
        get(l, m, V);
        get(m, r, V);
    }
}

int lg(int n) {
    return n == 1 ? 0 : __lg(n - 1) + 1;
}
int ceil(int n, int k) {
    return (n + k - 1) / k;
}

int solve(int l, int r, int n) {
    int s = l - 1;
    int k = r - l + 1;
    int ret = 0;
    if (s != 0) {
        int b = ceil(s, k);
        int os = 0, fs = 0;
        for (int i = 0; i <= __lg(b); i++) {
            if (b >> i & 1) os += 1 << i;
            else fs += 1 << i;
        }
        if (r + fs >= n) return 1e9;
        r += fs;
        ret += __lg(b) + 1;
    }
    return ret + lg(ceil(n, r));
}
int main() {
    cin.tie(0); ios_base::sync_with_stdio(0);
    
    int n, m;
    cin >> n >> m;
    int a[n + 1][m + 1]{};
    for (int i = 1; i <= n; i++) {
        string S;
        cin >> S;
        for (int j = 1; j <= m; j++) {
            a[i][j] = (S[j - 1] == '1');
        }
    }
    int ans = 1e9;
    int h[m + 2]{};
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (a[i][j]) h[j]++;
            else h[j] = 0;
        }
        h[0] = -2;
        h[m + 1] = -1;
        vector<int> S;
        S.push_back(0);
        for (int j = 1; j <= m + 1; j++) {
            while (!S.empty() && h[S.back()] >= h[j]) {
                int H = h[S.back()];
                S.pop_back();
                int prv = S.back() + 1;

                // solve (i - H + 1, i), (prv, j - 1)
                if (H != 0) {
                    int x1 = solve(i - H + 1, i, n);
                    int x2 = solve(n - i + 1, n - (i - H + 1) + 1, n);
                    int y1 = solve(prv, j - 1, m);
                    int y2 = solve(m - (j - 1) + 1, m - prv + 1, m);
                    ans = min(ans, min(x1, x2) + min(y1, y2));
                }
            }
            S.push_back(j);
        }
    }
    cout << ans << '\n';
}