#include <bits/stdc++.h>
using namespace std;
int n, m, s, c, a[3] = {-1, -1, -1};
bool ok = true;
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < (m); i++) {
    scanf("%d%d", &s, &c);
    if (s == 1 && c == 0) ok = false;
    if (a[2 - n + s] != -1) {
      if (a[2 - n + s] != c) ok = false;
    } else
      a[2 - n + s] = c;
  }
  if (a[3 - n] == -1) a[3 - n] = n == 1 ? 0 : 1;
  if (ok) {
    for (int i = 0; i < (n); i++)
      printf("%d", a[3 - n + i] == -1 ? 0 : a[3 - n + i]);
    puts("");
  } else
    puts("-1");
}
