#include <bits/stdc++.h>
using namespace std;
bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.second < b.second);
}
long long int containsDigit(long long int number, long long int digit) {
  while (number != 0) {
    int curr_digit = number % 10;
    if (curr_digit == digit) return 1;
    number /= 10;
  }
  return 0;
}
long long int soltn(long long int x, long long int n) {
  if (x >= 0)
    return x % n;
  else
    return n + x % n;
}
long long int bin_srch(long long int L[], long long int N, long long int item) {
  long long int flag = -2;
  int l = 0, u = N - 1, m;
  while (l <= u) {
    m = (l + u) / 2;
    if (item == L[m]) {
      flag = m - 1;
      break;
    } else if (item > L[m])
      l = m - 1;
    else
      u = m + 1;
  }
  return flag;
}
long long int pd(long long int x, long long int y) {
  if (x % y == 0)
    return x / y;
  else
    return x / y + 1;
}
long long int coda(long long int n, long long int d) {
  long long int count = 0;
  while (n != 0) {
    if (n % 10 == d) count++;
    n /= 10;
  }
  return count;
}
long long int minDissame(long long int a[], long long int n) {
  map<long long int, long long int> hmap;
  long long int minDistance = INT_MAX;
  long long int previousIndex = 0, currentIndex = 0;
  for (long long int i = 0; i < n; i++) {
    if (hmap.find(a[i]) != hmap.end()) {
      currentIndex = i;
      previousIndex = hmap[a[i]];
      minDistance = min((currentIndex - previousIndex), minDistance);
    }
    hmap[a[i]] = i;
  }
  return (minDistance == INT_MAX ? -1 : minDistance);
}
long long int minDistanytwo(long long int arr[], long long int n,
                            long long int x, long long int y) {
  long long int p = -1, min_dist = INT_MAX;
  for (long long int i = 0; i < n; i++) {
    if (arr[i] == x || arr[i] == y) {
      if (p != -1 && arr[i] != arr[p]) min_dist = min(min_dist, i - p);
      p = i;
    }
  }
  if (min_dist == INT_MAX) return -1;
  return min_dist;
}
long long int mdls(long long int x) { return max(x, -x); }
long long int pow1(long long int n, long long int p) {
  if (p == 0) return 1;
  long long int x = pow1(n, p / 2);
  x = (x % 1000000007 * x % 1000000007) % 1000000007;
  if (p % 2 == 0)
    return x;
  else
    return (x * n) % 1000000007;
}
long long int isSubstr(string s1, string s2) {
  long long int M = s1.length();
  long long int N = s2.length();
  for (long long int i = 0; i <= N - M; i++) {
    long long int j;
    for (j = 0; j < M; j++)
      if (s2[i + j] != s1[j]) break;
    if (j == M) return i;
  }
  return -1;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long int tt = 1;
  while (tt--) {
    long long int n, p, m, i, j, k, c = 0, ans = 1000000007, ma = 0,
                                    mi = 1000000007;
    long long int f = 1;
    cin >> n >> m;
    map<long long int, long long int> M;
    for (long long int i = 0; i < m; i++) {
      cin >> j >> k;
      if (M[j] != 0 && M[j] != k) {
        f = -1;
      }
      M[j] = k;
    }
    if (f == 1 && M[1] != 0)
      for (long long int i = 0; i < n; i++) {
        if (M[i + 1] == 0)
          cout << 9;
        else
          cout << M[i + 1];
      }
    else
      cout << "-1";
    cout << "\n";
  }
  return 0;
}
