#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
using namespace std;
long long max3(long long x, long long y, long long z) {
  return max(max(x, y), z);
}
long long min3(long long x, long long y, long long z) {
  return min(min(x, y), z);
}
const long long N = 1e5 + 10, M = 2e5 + 10, M2 = 1e6 + 10, mod = 1e9 + 7,
                inf = 1e17 + 10;
const long long INF = 1e9 + 7;
void add(long long &a, long long b) {
  a += b;
  if (a >= mod) {
    a -= mod;
  }
}
template <typename Arg1>
void __f(const char *name, Arg1 &&arg1) {
  cerr << name << " : " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char *names, Arg1 &&arg1, Args &&...args) {
  const char *comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
long long X[] = {0, 1, 0, -1};
long long Y[] = {-1, 0, 1, 0};
long long power(long long x, long long n) {
  long long result = 1;
  while (n > 0) {
    if (n % 2 == 1) result = (result * x) % mod;
    x = ((x % mod) * (x % mod)) % mod;
    n = n / 2;
  }
  return result;
}
long long n, m;
long long x[4];
map<long long, long long> mp;
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  for (long long i = 1; i < m + 1; i++) {
    long long a, b;
    cin >> a >> b;
    if (mp[a] && x[a] != b) {
      cout << -1;
      return 0;
    } else {
      x[a] = b;
      mp[a]++;
    }
  }
  if (x[1] == 0 && n != 1 && mp[1]) {
    cout << -1;
    return 0;
  }
  if (x[1] == 0) x[1] = 1;
  for (long long i = 1; i <= n; i++) cout << x[i];
  return 0;
}
