#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long mod2 = 998244353;
long long mod3 = 1000003;
long long mod4 = 998244853;
long long mod5 = 1000000009;
long long inf = 1LL << 60;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-10;
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
long long gcd(long long a, long long b) {
  if (a < b) swap(a, b);
  if (b == 0) return a;
  if (a % b == 0) return b;
  return gcd(b, a % b);
}
long long Pow(long long n, long long k) {
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k & 1) ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
long long beki(long long n, long long k, long long md) {
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
long long gyaku(long long n, long long md) { return beki(n, md - 2, md); }
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  int m;
  cin >> m;
  int s[m], c[m];
  for (long long i = 0; i < m; i++) cin >> s[i] >> c[i];
  int ue = Pow(10, n);
  for (long long i = 0; i < ue; i++) {
    int a[n];
    int now = i;
    int l = 0;
    for (long long j = n - 1; j >= 0; j--) {
      a[j] = now % 10;
      now /= 10;
    }
    while (l < n && a[l] == 0) l++;
    int cc = 0;
    for (long long j = 0; j < m; j++) {
      if (s[j] <= l) {
        cc = 1;
        break;
      }
      if (a[s[j] - 1] != c[j]) {
        cc = 1;
        break;
      }
    }
    if (cc == 0) {
      cout << i << endl;
      return 0;
    }
  }
  cout << -1 << endl;
}
