#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll read(){
	int a=0,b=getchar();
	while(!isdigit(b))b=getchar();
	while(isdigit(b))a=a*10+b-'0',b=getchar();
	return a;
}
int n,m,a[5];
int main(){
	memset(a,-1,sizeof(a));
	n=read(),m=read();
	while(m--){
		int x=read(),y=read();
		if(a[x]!=-1 and a[x]!=y)return puts("-1"),0;
		a[x]=y;
	}
	if(n!=1 and a[1]==0)return puts("-1"),0;
	for(int i=1;i<=n;i++){
		if(a[i]!=-1)cout << a[i];
		else if(i!=1 or n==1)cout << 0;
		else cout << 1;
	}
	return 0;
}