#include<bits/stdc++.h>

using namespace std;


int main(){
    int s[3] = {0,0,0};
    bool flag = true;
    int n,m ,x ,y ,num = 0;

    cin >> n >> m;

    for (int i = 0; i < m; i++){
        cin >> x >> y;

        if(s[x-1]!=0 && s[x-1]!=y)
            flag = false;
        
        s[x-1] = y;
        
    }
    for (int i = 0; i < n; i++)
    {
        num+= (int)pow(10,i)*s[n-i-1];
        
    }
    if(num == 0 || s[0] == 0{
        flag = false;
    }
    if(flag){
        cout<< num << "\n";
    }
    else{
        cout<< "-1" << "\n";
    }
    
   
}