#include <bits/stdc++.h>

using namespace std;

int main() {
    int N, M;
    cin >> N >> M;
    pair<int, int> sc[M];

    int s, c;
    for (int i = 0; i < M; i++){
        cin >> s >> c;
        sc[i] = pair<int, int>(s, c);
    }

    for( int i = pow(10, N - 1); i < pow(10, N); i++){
        bool success = true;
        string s = to_string(i);
        for (pair<int, int> p : sc){
            if (stoi(""s + s.at(p.first - 1)) != p.second) {
                success = false;
                break;
            }
        }
        if (success){
            cout << i << endl;
            return 0;
        }
    }
    cout << "-1" << endl;

    return 0;
}