#include<cstdio>
struct node{
	int s,c;
} a[100];
int n,m,ans[100];
int main() {
	scanf("%d%d",&n,&m);
	for (int i=1;i<=m;++i) scanf("%d%d",&a[i].s,&a[i].c);
	for (int i=1;i<=m;++i) if (!ans[a[i].s]) ans[a[i].s]=a[i].c; else if (ans[a[i].s]!=a[i].c) ans[0]=-1;
	if (n>1) for (int i=1;i<=m;++i) if (a[i].s==1&&a[i].c==0) ans[0]=-1;
	if (n>1&&!ans[1]) ans[1]=1;
	if (ans[0]==-1) {
		printf("-1");
		return 0;
	}
	for (int i=1;i<=n;++i) printf("%d",ans[i]);
	return 0;
} 