#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f, N = 2e6 + 5, MOD = 1e9 + 7;
const long long INF_LL = 0x3f3f3f3f3f3f3f3fLL;
inline int getplc(int x, int y) { return (x >> y) & 1; }
template <typename T>
T square(T x) {
  return x * x;
}
long long qpow(long long a, long long b = MOD - 2, long long _MOD = MOD) {
  long long res = 1;
  for (; b; b >>= 1, a = a * a % _MOD) {
    if (b & 1) res = res * a % _MOD;
  }
  return res;
}
template <typename T>
T Smax(T x) {
  return x;
}
template <typename T, typename... Args>
T Smax(T a, Args... args) {
  return max(a, Smax(args...));
}
template <typename T>
T Smin(T x) {
  return x;
}
template <typename T, typename... Args>
T Smin(T a, Args... args) {
  return min(a, Smin(args...));
}
template <typename T>
void errl(istream_iterator<string> it) {}
template <typename T, typename... Args>
void errl(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " = " << a << endl;
  errl(++it, args...);
}
void err(istream_iterator<string> it) {}
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << "=" << a << " # ";
  err(++it, args...);
}
void Solve();
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  Solve();
  return 0;
}
char s[4][N];
int f[N][10], g[10][10], w[N][10];
int check(int a, int b, int n) {
  for (int i = 1; i <= n - 1; i++) {
    int black = 0;
    if (getplc(a, i - 1)) black++;
    if (getplc(a, i)) black++;
    if (getplc(b, i - 1)) black++;
    if (getplc(b, i)) black++;
    if (black % 2 == 0) return 0;
  }
  return 1;
}
void Solve() {
  int n, m;
  cin >> n >> m;
  if (n >= 4) {
    cout << -1 << endl;
    return;
  }
  memset(f, 0x3f, sizeof f);
  for (int i = 1; i <= n; i++) {
    cin >> s[i] + 1;
    for (int j = 1; j <= m; j++) s[i][j] -= '0';
  }
  int lim = (1 << (n)) - 1;
  for (int i = 0; i <= lim; i++) {
    for (int j = 0; j <= lim; j++) g[i][j] = check(i, j, n);
  }
  for (int i = 0; i <= lim; i++) {
    f[1][i] = 0;
    for (int j = 1; j <= n; j++)
      if (getplc(i, j - 1) ^ s[j][1]) f[1][i]++;
  }
  for (int p = 1; p <= m; p++) {
    for (int i = 0; i <= lim; i++) {
      for (int j = 1; j <= n; j++)
        if (getplc(i, j - 1) ^ s[j][p]) w[p][i]++;
    }
  }
  for (int i = 2; i <= m; i++) {
    for (int pre = 0; pre <= lim; pre++) {
      for (int now = 0; now <= lim; now++) {
        if (g[pre][now]) {
          f[i][now] = min(f[i][now], f[i - 1][pre] + w[i][now]);
        }
      }
    }
  }
  int ans = INF;
  for (int i = 0; i <= lim; i++) ans = min(ans, f[m][i]);
  cout << ans << endl;
}
