v#include <bits/stdc++.h>

using namespace std;

int main(){
    int N, M;
    cin >> N >> M;

    vector<int> s(M), c(M);
    for (int i = 0; i < M; i++){
        cin >> s.at(i) >> c.at(i);
    }

    int min = 0;
    if ((N == 2) || (N == 3)){
        min = pow(10,N-1);
    }
    
    if (M == 0){
        cout << min << endl;
        return 0;
    }

    for (int n = 0; n < 1000; n++){ 
        string n_str = to_string(n);
        int len = (int)(n_str.length());
        if (len != N) continue;
        if (len == 1) n_str = "00" + n_str;
        if (len == 2) n_str = "0" + n_str;
        bool ok = true;
        for (int i = 0; i < M; i++){
            if (n_str[s[i]-1] != (char)('0'+c[i])){
                ok = false;
            }
        }
        if (ok){
            cout << n << endl;
            return 0;
        }
    }

    cout << -1 << endl;

    return 0;
}
