#include<bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
typedef long long LL;
const int MAXN = 100000 + 3;
int a[5], n, m, p, d;

int main() {
  	memset(a, -1, sizeof(a));
    cin>>n>>m;
  	for(int i=0;i<m;i++) {
    	cin>>p>>d;
        p --;
        if(a[p] != -1) {
        	printf("-1\n");
          return 0;
        }
      a[p] = d;
    }
    if(a[0] == 0 && n > 1) {
      printf("-1\n");
          return 0;
    }
    if(a[0] == -1)a[0] = 1;
  int ans = 0;
  for(int i=0;i<n;i++) {
    if(a[i] == -1) a[i] = 0;
  	ans = ans * 10 + a[i];
  }
  cout<<a[i]<<endl;
    return 0;
}
