#include <iostream>
#include <vector>
using namespace std;
int main(){
	int n,m;
	int a[3];
	cin>>n>>m;
	a[0]=-1;
	a[1]=-1;
	a[2]=-1;
	for(int i=0;i<m;i++){
		int s,c;
		cin>>s>>c;
		if(a[s-1]==-1){
			a[s-1]=c;
		}else{
			if(a[s-1]==c){
				continue;
			}else{
				cout<<-1<<endl;
				return 0;
			}
		}
	}
	if(a[0]==0){
		if(n==1){
			cout<<0<<<endl;
		}else{
			cout<<-1<<endl;
		}
		return 0;
	}
	if(n==1){
		if(a[0]==-1){
			cout<<0<<endl;
		}else{
			cout<<a[0]<<endl;
		}
		return 0;
	}
	for(int i=0;i<n;i++){
		if(a[i]==-1){
			if(i==0){
				cout<<1;
			}else{
				cout<<0;
			}
		}else{
			cout<<a[i];
		}
	}
	cout<<endl;
	return 0;
}