#include <iostream>
#include <vector>

using namespace std;

int n, m, s;
char c;

std::vector<char> vec;

int main() {
    std::cin >> n >> m;
    vec.assign(n+1, '~');
    for (int i = 0; i < m; i++) {
        std::cin >> s >> c;
        if (vec[s] != '~' && vec[s] != c || (s == 1 && c == '0') {
            cout << -1 << endl;
            return 0;
        }
        vec[s] = c;
    }
    for (int i = 1; i < vec.size(); i++) {
        if (i == 1 && vec[i] == '~') {
            vec[i] = '1';
        }
        else if (vec[i] == '~') {
            vec[i] = '0';
        }
        cout << vec[i];
    }
    cout << '\n';
    
    
}