#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
int n,m,s,c,a[3] = {-1,-1,-1};
bool ok = true;
int main(){
	scanf("%d%d", &n, &m);
	rep(i,m){
		scanf("%d%d", &s, &c);
		if(s == 1 && c == 0 && n > 1) ok = false;
		if(a[2-n+s] != -1){
			if(a[2-n+s] != c) ok = false;
		}else a[2-n+s] = c;
	}
	if(a[3-n] == -1) a[3-n] = n == 1 ? 0 : 1;
	if(ok){
		rep(i,n) printf("%d",a[3-n+i] == -1 ? 0 : a[3-n+i]);
		puts("");
	}else puts("-1");
}