#include <iostream>
#include <cstdio>
#include <vector>
using namespace std;

int main(){
    int n,m;
    int s[3];
    cin  >> n >> m;
    int t1,t2;
    s[0]=-1;
    s[1]=-1;
    s[2]=-1;
    bool flag = 0;
    for(int i=0;i<m;i++){
        cin >> t1 >> t2;
        if(s[t1-1] == -1)s[t1-1] = t2;
        else if(s[t1-1] != t2)flag = 1;
    }

    if(n == 1){
        if(s[1] != -1 || s[2] != -1)flag = 1;
        if(flag){
            cout << -1 << endl;
            return 0;
        }
        if(s[0] == -1)s[0] = 0;
        cout << s[0] <<endl;
        return 0;
    }

    if(n == 2){
        if(s[2] != -1 || s[0] == 0)flag = 1;
        if(s[0] == -1)s[0]=1;
        if(s[1] == -1)s[1]=0;
        
        if(flag){
            cout << -1 << endl;
            return 0;
        }
        cout << s[0]*10+s[1] << endl;
        return 0;
    }

    if(n == 3){
        if(s[0] == 0)flag=1;
        if(flag){
            cout <<-1 << endl;
            return 0;
        }
            if(s[0] == -1)s[0]=1;
            if(s[1] == -1)s[1]=0;
            if(s[2] == -1)s[2]=0;
            cout << s[0]*100+s[1]*10+s[2] <<endl;
            return 0;
        
       
}