int N, M;
vector<int> s, c;

bool ok(string str) {
    if (str.size() != N) return false;
    for (int i = 0; i < M; ++i) if (str[s[i]] != (char)(c[i] + '0')) return false;
    return true;
}

string solve() {
    for (int i = 0; i <= 999; ++i) {
        stringstream iss; iss << i;
        string str = iss.str();
        if (ok(str)) return str;
    }
    return "-1";
}

int main() {
    cin >> N >> M;
    s.resize(M); c.resize(M);
    for (int i = 0; i < M; ++i) cin >> s[i] >> c[i], --s[i];
    cout << solve() << endl;
}