#include<bits/stdc++.h>
using namespace std;

int N,M,s[5],c[5];
string S;

int main(){
	cin>>N>>M;
	S=string(N,0);
	for(int i=0;i<M;i++){
		cin>>s[i]>>c[i];
		s[i]--;
		if(N!=1&&s[i]==0&&c[i]==0){
			cout<<-1<<endl;
			return 0;
		}
		if(S[s[i]]==0||S[s[i]]=='0'+c[i]){
			S[s[i]]='0'+c[i];
		}
		else{
			cout<<-1<<endl;
			return 0;
		}
	}
	for(int i=0;i<N;i++){
		if(S[i]==0){
			if(i==0&&N!=1)cout<<1;
			else cout<<0;
		}
		else cout<<S[i];
	}
	cout<<endl;
}
