#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimization("unroll-loops")
#pragma GCC optimize("O2")
constexpr int dx[] = {-1, 0, 1, 0, 1, 1, -1, -1};
constexpr int dy[] = {0, -1, 0, 1, 1, -1, 1, -1};
constexpr long long INF = 1999999999999999997;
constexpr int inf = INT_MAX;
constexpr int MAXSIZE = int(1e6) + 5;
constexpr auto PI = 3.14159265358979323846L;
constexpr auto oo = numeric_limits<int>::max() / 2 - 2;
constexpr auto eps = 1e-6;
constexpr auto mod = 1000000007;
constexpr auto MOD = 1000000007;
constexpr auto MOD9 = 1000000009;
constexpr auto maxn = 100006;
void fastio() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
int main() {
  fastio();
  int n, m;
  cin >> n >> m;
  vector<int> v(n, -1);
  bool ok = true;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    a--;
    if (v[a] == -1) {
      v[a] = b;
    } else if (v[a] != b) {
      ok = false;
    }
  }
  for (int i = 0; i < n; i++) {
    if (v[i] == -1) v[i] = 1;
  }
  int check = 0;
  for (int i = 0; i < n; i++) {
    if (v[i] != 0) {
      check = v[i];
      break;
    }
    if (check == 0 && v[i] == 0) {
      ok = false;
      break;
    }
  }
  if (ok) {
    for (auto i : v) cout << i;
  } else
    cout << "-1";
}
