#include<bits/stdc++.h>
using namespace std;
string s1,s2;
int n=0;
int main(){
	cin>>s1>>s2;
	int len1 = s1.size(),len2 = s2.size();
	if(len1>=len2)
		if(s1.find(s2)!=-1) n=1;
	else
		if(s2.find(s1)!=-1) n=2;
	if(n==1)
		cout<<s2+" is substring of "+s1;
	else if(n==2)
		cout<<s1+" is substring of "+s2;
	else cout<<"No substring";
	return 0;
}