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

int main(){

	int n,m,s,c;
	cin >> n >> m;
	vector<int> v(n,-1);
	
	while(m--){
		cin >> s >> c;
		if(v[s-1] == -1 || v[s-1]==c) v[s-1] = c;
		else{cout << -1; return 0;}
	}
	if(n==1 && (v[0]==-1 || v[0]==0)) {cout << 0; return 0;}
	if(v[0]==0) {cout << -1; return 0;}
	if(v[0]==-1) v[0]=1;
	int result = 0;
	for(auto x:v) {result = result*10 + (x==-1 ? 0 : x);}
	cout << result;
}
