#include <cstdio>
#include <cmath>
using namespace std;
int N, M, s[10], c[10];
int main() {
  scanf("%d %d", &N, &M);
  for(int i = 1; i <= M; ++i) scanf("%d %d", &s[i], &c[i]);
  int st = N>1?pow(10, N-1):0, ans = -1;
  for(int i = st; i <= pow(10, N)-1; ++i) {
    int num[3] = {i/100, (i%100)/10, (i%10)/1}, cnt = 0;
    for(int j = 1; j <= M; ++j) {
      if(num[s[j]-N+2] == c[j]) ++cnt;
    }
    if(cnt != M) continue;
    ans = i;
    break;
  }
  printf("%d\n", ans);
}