#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
#define print(x) cout<<'>'<<#x<<':'<<x<<endl;
#define F first
#define S second
const int mod=1000000007;

void solve(){
    int n,m;
    cin>>n>>m;
    int s[m];char c[m];
    string num="";
    for (int i=0;i<n;i++)num+="0";
    for (int i=0;i<m;i++)cin>>s[i]>>c[i];
    for (int i=0;i<m;i++){
        if (s[i]>n){
            cout<<-1<<endl;
            return;
        }else{
            if ((c[i]==0)&&(s[i]==1)){
                if (n!=1)(cout<<-1<<endl;return;}
            }
            if (num[s[i]-1]!=c[i]){
                if (num[s[i]-1]!='0'){
                    cout<<-1<<endl;
                    return;
                }else{
                    num[s[i]-1]=c[i];
                }
            }
        }
    }if (num[0]=='0'){
        if (n==1){cout<<0<<endl;return;}
        else num[0]='1';
    }cout<<num<<endl;
}

int main()
{
    ios_base::sync_with_stdio(false);cin.tie(NULL);

    solve();

    return 0;
}
