#include "bits/stdc++.h"

using namespace std;

void Main() {
    int N, M;
    cin >> N >> M;
    map<int, int> digitNum;
    for (int i = 0; i < M; ++i) {
        int s, c;
        cin >> s >> c;
        if (digitNum.count(s) != 0 && digitNum[s] != c) {
            cout << -1 << endl;
            return;
        }
        digitNum.insert(make_pair(s, c));
    }

    if (N == 1) {
        if (digitNum.size() == 0) {
            cout << 0 << endl;
            return;
        }
        else {
            auto e = digitNum.begin();
            cout << (e->second) << endl;
            return;
        }
    }
    else if (N == 2) {
        if (digitNum.size() == 0) {
            cout << 10 << endl;
            return;
        }
        else if (digitNum.size() == 1) {
            if (digitNum.count(1) == 1) {
                if (digitNum[1] == 0) {
                    cout << -1 << endl;
                    return;
                }
                else {
                    cout << digitNum[1] << 0 << endl;
                    return;
                }
            }
            else { // digitNum.count(2) == 1
                cout << 1 << digitNum[2] << endl;
                return;
            }
        }
        else {
            if (digitNum[1] == 0) {
                cout << -1 << endl;
                return;
            }
            else {
                cout << digitNum[1] << digitNum[2] << endl;
                return;
            }
        }
    }
    else { // N == 3
        if (digitNum.size() == 0) {
            cout << 100 << endl;
            return;
        }
        else if (digitNum.size() == 1) {
            if (digitNum.count(1) == 1) {
                if (digitNum[1] == 0) {
                    cout << -1 << endl;
                    return;
                }
                else {
                    cout << digitNum[1] << 0 << 0 << endl;
                    return;
                }
            }
            else if (digitNum.count(2) == 1) {
                cout << 1 << digitNum[2] << 0 << endl;
                return;
            }
            else { // digitNum.count(3) == 1
                cout << 1 << 0 << digitNum[3] << endl;
                return;
            }
        }
        else if (digitNum.size() == 2) {
            if (digitNum.count(1) == 0) {
                cout << 1 << digitNum[2] << digitNum[3] << endl;
                return;
            }
            else if (digitNum.count(2) == 0) {
                if (digitNum[1] == 0) {
                    cout << -1 << endl;
                    return;
                }
                else {
                    cout << digitNum[1] << 0 << digitNum[3] << endl;
                    return;
                }
            }
            else { // digitNum.count(3) == 0
                if (digitNum[1] == 0) {
                    cout << -1 << endl;
                    return;
                }
                else {
                    cout << digitNum[1] << digitNum[2] << 0 << endl;
                    return;
                }
            }
        }
        else {
            if (digitNum[1] == 0) {
                cout << -1 << endl;
                return;
            }
            else {
                cout << digitNum[1] << digitNum[2] << digitNum[3] << endl;
            }
        }
    }
    return;
}

int main() {
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}


Measured memory_bytes: 256