#include<iostream>
#include<iomanip>
#include<cmath>
#include<cstring>
using namespace std;
int main(){
	char s1[201]={};
	char s2[201]={};
	cin>>s1;
	cin>>s2;
	int a=strlen(s1);
	int b=strlen(s2);
	int n=0;
	if(a<b){
		for(int i=0;i<b;i++){
			if(s2[i]==s1[0]){
				for(int j=0;j<a;j++){
					
					if(s1[j]==s2[i+n]){
						n=n+1;
					}
					else{
						break;
					}
			}
			}
		}
		if(a==n){
		cout<<s1<<" is substring of "<<s2;
	}
	else{
		cout<<"NO";
	}
	}
	
	else{
		for(int i=0;i<a;i++){
			if(s1[i]==s2[0]){
				for(int j=0;j<b;j++){
					
					if(s2[j]==s1[i+n]){
						n=n+1;
					}
					else{
						break;
					}
			}
			}
		}
		if(b==n){
		cout<<s2<<" is substring of "<<s1;
	}
	else{
		cout<<"No substring";
	}
	}
	
	return 0;
}