#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T BM(T p, T e, T M) {
  long long int ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p) % M;
    p = (p * p) % M;
  }
  return (T)ret;
}
template <class T>
inline T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
template <class T>
inline T mdINV(T a, T M) {
  return BM(a, M - 2, M);
}
template <class T>
inline T PW(T p, T e) {
  long long int ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p);
    p = (p * p);
  }
  return (T)ret;
}
template <class T>
bool ISLEFT(T a, T b, T c) {
  if (((a.first.first - b.first.first) * (b.second.second - c.second.second) -
       (b.first.first - c.first.first) * (a.second.second - b.second.second)) <
      0.0)
    return 1;
  else
    return 0;
}
int main() {
  int n, m;
  cin >> n >> m;
  int ar[n + 2];
  for (int i = 1; i <= n; i++) ar[i] = -1;
  for (int i = 1; i <= m; i++) {
    int first, second;
    scanf("%d%d", &first, &second);
    if (ar[first] == -1 || ar[first] == second)
      ar[first] = second;
    else {
      cout << (-1) << endl;
      return 0;
    }
  }
  if (ar[1] == 0)
    cout << (-1) << endl;
  else {
    if (ar[1] == -1) ar[1] = 1;
    for (int i = 1; i <= n; i++) {
      if (ar[i] == -1) ar[i] = 0;
      cout << ar[i];
    }
    cout << endl;
  }
  return 0;
}
