#include <bits/stdc++.h>
using namespace std;
int dp[2010][2010], k[2010][2010];
int main() {
  int n, m;
  string a;
  scanf("%d %d", &n, &m);
  memset(dp, 0, sizeof(dp));
  memset(k, 0, sizeof(k));
  for (int x = 0; x < n; x++) {
    cin >> a;
    for (int y = 0; y < m; y++) {
      int i;
      k[x][y] = a[y] - '0';
      dp[x + 1][y] = dp[x][y] + k[x][y];
    }
  }
  bool flag = false, ch = true;
  for (int x = 0; x < n; x++) {
    ch = true;
    for (int y = 0; y < m; y++) {
      if (dp[n][y] - k[x][y] == 0) {
        ch = false;
        break;
      }
    }
    if (ch) {
      flag = true;
      break;
    }
  }
  if (ch)
    cout << "yes";
  else
    cout << "no";
  return 0;
}
