nt main(){
    int n,m;
    cin >> n >> m;
    vector<pair<int,int> > a(m);
    for (int i = 0; i  < m; i++) {
        cin >> a[i].first >> a[i].second;
    }
    for (int i = 1; i < 1000; i++) {
        int keta = 1;
        int nx = i/10;
        vector<int> d(1,i%10);
        while (nx) {
            keta++;
            d.push_back(nx%10);
            nx /= 10;
        }
        if (keta != n) continue;
        bool ans = true;
        reverse(d.begin(), d.end());
        for (int j = 0; j < m; j++) {
            if (d[a[j].first-1] != a[j].second) ans = false;
        }
        if (ans) {
            cout << i << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return 0;

}