#include<bits/stdc++.h>
using namespace std ;
#define pb push_back
#define endl '\n'
#define x first
#define y second

int main(){
	int n,m,s,c;
	int a[4]={-1,-1,-1,-1};
	cin>>n>>m;
	bool f=0;
	while(m--){
		cin>>s>>c;
		s--;
		if(a[s]!=-1){
			if(a[s]!=c)f=1;
		}
		a[s]=c;
	}
	if(f){
		cout<<-1<<endl;
		return 0;
	}
	if(n!=1 &&a[0]==0){
		cout<<-1<<endl;
		return 0;
	}
	if(a[0]==-1){
		if(n==1){
			a[0]=0;
		}else{
			a[0]=1;
		}
	}
	for(int i=0;i<n;i++){
		if(a[i]==-1){
			a[i]=0;
		}
		cout<<a[i];
	}
	cout<<endl;
}