#include <stdio.h>
#include <map>
using namespace std;

int main() {
    int n, m;
    scanf("%d", &n);
    scanf("%d", &m);

    bool flag = true;
    int s, c;
    map<int, int> b;
    for (int i=0; i<m; i++) {
        scanf("%d", &s);
        scanf("%d", &c);
        if (s == 1 and c == 0) {
            flag = false;
            break;
        }
        if (b.count(s)) {
            if (b[s] != c) {
                flag = false;
                break;
            }
        }
        b[s] = c;
    }

    if (flag) {
        if (not b.count(1)) {
            if (n == 1) {
                b[1] = 0;
            } else {
                b[1] = 1;
            }
        }
        int ans[n] = {};
        for(auto i = b.begin(); i != b.end(); ++i) {
            ans[i->first - 1] = i->second;
        }
        for (int i=0; i<n; i++) {
            printf("%d", ans[i]);
        }
        printf("\n");
    } else {
        printf("-1\n");
    }
}