#include <bits/stdc++.h>
#define rep(i,n) for (i=0;i<(n);++i)
using namespace std;
using P = pair<int,int>;

int main(){
    int n,m;
    cin >> n >> m;
    vector<P> p(m);
    
    rep(i,m) cin >>p[i].first >>p[i].second;

    rep(x,1000){
        int keta = 1;
        int nx = x/10;
        vector<int> d(1,x%10);
        while(nx){
            keta++;
            d.push_back(nx%10);
            nx/=10;
        }
        if(keta != n) continue;
        bool ok =true;
        reverse(d.begin(), d.end());
        rep(i,m){
            if(d[p[i].first-1]!= p[i].second) ok =false;
        }
        if(ok){
            cout << x << endl;
            return 0;
        }
        }
    cout << -1 << endl;
    return 0;
}