#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
 
 
int main() {
 
	int n, m;
 
	scanf("%d %d", &n, &m);
 
	int tmp[3] = {10, 10, 10};
	int s[5];
	int c[5];
 
	for(int i = 0; i < m; i++) {
		scanf("%d %d", &s[i], &c[i]);
	}
 
 
	for(int i = 0; i < m; i++) {
		if( (tmp[s[i] -1]) == 10) {
			tmp[s[i] -1] = c[i];
		}
		else if( (tmp[s[i] -1]) == c[i]){
			continue;
		}
		else{
			printf("-1\n");
			return 0;
		}
	}
 
	for(int i = 0; i < n; i++) {
		if(tmp[i-1] == 10) {
			tmp[i-1] = 0;
		}
	}
 
	int ans = 0;
	if(n == 3) {
		for(int i = 0; i < m; i++) {
			if( (s[i] == 1) && (c[i] == 0) ){
				printf("-1\n");
				return 0;
			}
		}
		ans = tmp[0] * 100 + tmp[1] * 10 + tmp[2];
	} else if( n == 2) {
		for(int i = 0; i < m; i++) {
			if( (s[i] == 1) && (c[i] == 0) ){
				printf("-1\n");
				return 0;
			}
		}
		ans = tmp[0] * 10 + tmp[1];
	} else if( n == 1) {
		for(int i = 0; i < m; i++) {
			if(c[i] == 0){
				printf("-1\n");
				return 0;
			}
		}
		ans = tmp [0];
	}
 
 
	printf("%d", ans);
 
	return 0;
 
}
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>


int main() {

	int n, m;

	scanf("%d %d", &n, &m);

	int tmp[3] = {10, 10, 10};
	int s[5];
	int c[5];

	for(int i = 0; i < m; i++) {
		scanf("%d %d", &s[i], &c[i]);
	}


	for(int i = 0; i < m; i++) {
		if( (tmp[s[i] -1]) == 10) {
			tmp[s[i] -1] = c[i];
		}
		else if( (tmp[s[i] -1]) == c[i]){
			continue;
		}
		else{
			printf("-1\n");
			return 0;
		}
	}

	for(int i = 0; i < n; i++) {
		if(tmp[i-1] == 10) {
			tmp[i-1] = 0;
		}
	}

	int ans = 0;
	if(n == 3) {
		for(int i = 0; i < m; i++) {
			if( (s[i] == 1) && (c[i] == 0) ){
				printf("-1\n");
				return 0;
			}
		}
		ans = tmp[0] * 100 + tmp[1] * 10 + tmp[2];
	} else if( n == 2) {
		for(int i = 0; i < m; i++) {
			if( (s[i] == 1) && (c[i] == 0) ){
				printf("-1\n");
				return 0;
			}
		}
		ans = tmp[0] * 10 + tmp[1];
	} else if( n == 1) {

		ans = tmp [0];
	}


	printf("%d", ans);

	return 0;

}