#include <bits/stdc++.h>
using namespace std;
template <class c>
struct rge {
  c b, e;
};
template <class c>
rge<c> range(c i, c j) {
  return rge<c>{i, j};
}
template <class c>
auto dud(c* x) -> decltype(cerr << *x, 0);
template <class c>
char dud(...);
struct debug {
  template <class c>
  debug& operator<<(const c&) {
    return *this;
  }
};
const long long int N = 2e5 + 5;
long long int mod = 1e9 + 7;
long long int dx[4] = {0, 0, +1, -1};
long long int dy[4] = {+1, -1, 0, 0};
long long int po(long long int a, long long int b) {
  a %= mod;
  long long int res = 1;
  while (b > 0) {
    if (b & 1) res = (res * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return res;
}
set<long long int> v[3];
void solve() {
  long long int n, m;
  cin >> n >> m;
  vector<long long int> ans(n, 0);
  for (long long int i = 0; i < m; i++) {
    long long int x, y;
    cin >> x >> y;
    --x;
    v[x].insert(y);
  }
  for (long long int i = 0; i < n; i++) {
    if ((long long int)v[i].size() > 1) {
      cout << -1 << "\n";
      return;
    }
  }
  for (long long int i = 0; i < n; i++) {
    if ((long long int)v[i].size()) {
      ans[i] = *v[i].begin();
    }
  }
  if (n != 1 && ans[0] == 0)
    cout << -1 << "\n";
  else {
    for (long long int i = 0; i < n; i++) cout << ans[i];
    cout << "\n";
  }
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int t = 1;
  while (t--) solve();
  return 0;
}
