#include <bits/stdc++.h>
#define LL long long
using namespace std;
const int maxn = 1e5+5;

int n, m, a[10];
int main(){
    cin >> n >> m;

    memset(a, -1, sizeof a);
    int x, y, f=1;
    while(m--){
        cin >> x >> y;
        if(a[x] != -1 && a[x] != y) f = 0;
        else a[x] = y;
    }
    if(f==0 || (n>1 && a[1]==0)) puts("-1");
    else {
        if(n>1 && a[1]==-1) a[1] = 1;
        for(int i=1; i<=n; i++) cout << max(0,a[i]); cout << endl;
    }
}