#include<bits/stdc++.h>

using namespace std;



int main() {

    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);

   int n,m,x,y;
   int a,b,c;

   cin>>n>>m;

   a = 0;
   b = 0;
   c = 0;

   int flaga = 0, flagb = 0, flagc = 0;
    int flag = 0;

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

        if(x==1){
            if(flaga == 1){
               if(a != y) flag = 1;
            }

            a = y;
            flaga = 1;
        }
        if(x==2){
            if(flagb == 1){
               if(b != y) flag = 1;
            }

            b = y;
            flagb = 1;
        }
        if(x==3){
            if(flagc == 1){
               if(c != y) flag = 1;
            }
            c = y;
            flagc = 1;
        }

   }

    if(flag==1) {
        cout<<-1<<endl;
        return 0;
    }

   if(n==1){
        cout<<a<<endl;
        return 0;
   }

   if(n==2){
        if(a == 0) cout<<-1<<endl;
        else{

            for(int i=10;i<100;i++){
                int tmp = i;
                int ta = tmp%10;
                tmp /= 10;
                if(tmp == a %% ta==b){
                    cout<<i<<endl;
                    return 0;
                }
            }

        }

        return 0;
   }


    if(a == 0){
        cout<<-1<<endl;
        return 0;
    }

    for(int i=100;i<1000;i++){
        int tmp = i;
        int tc = tmp%10;
        tmp /= 10;
        int tb = tmp%10;
        tmp /= 10;

        if(tc == c && tb == b && tmp==a){
            cout<<i<<endl;
            return 0;
        }

    }

    return 0;
}
