#include <bits/stdc++.h>
using namespace std;
long long read() {
  int a = 0, b = getchar();
  while (!isdigit(b)) b = getchar();
  while (isdigit(b)) a = a * 10 + b - '0', b = getchar();
  return a;
}
int n, m, a[5];
int main() {
  memset(a, -1, sizeof(a));
  n = read(), m = read();
  while (m--) {
    int x = read(), y = read();
    if (a[x] != -1 and a[x] != y) return puts("-1"), 0;
    a[x] = y;
  }
  if (n != 1 and a[1] == 0) return puts("-1"), 0;
  for (int i = 1; i <= n; i++) {
    if (a[i] != -1)
      cout << a[i];
    else if (i != 1)
      cout << 0;
    else
      cout << 1;
  }
  return 0;
}
