#include <bits/stdc++.h>
#define int long long
using namespace std;
string k,k1;bool flag=0;
signed main(){
	cin>>k>>k1;
	int s=k.size(),s1=k1.size(),t=max(s,s1),t1=min(s1,s);
	for(int j=0;j<t;j++){
		for(int i=j;i<t1;i++){
			if(k[i]!=k1[i]){
				flag=1;break;	
			}
		}
		if(flag==0){
			if(t==s)cout<<k1<<" is substring of "<<k;
			else if(t1==s)cout<<k<<" is substring of "<<k1;
			return 0;
		}
		flag=0;
	}
	cout<<"No substring";
	return 0;	
}