#include<bits/stdc++.h>
using namespace std;
int main(){
	char a1[205],a2[205];
	cin>>a1>>a2;
	int s1=strlen(a1);
	int s2=strlen(a2);
	int s3=0,s4=0;
	for(int i=0;i<max(s1,s2);i++){
		s4=i;
		if(i<=max(s1,s2)-min(s1,s2)){
			for(int j=0;j<min(s1,s2);j++){
				if(s1<=s2){
					if(a1[j]==a2[s4]){
						s4++;
					}
				}else{
					if(a2[j]==a1[s4]){
						s4++;
					}else{
						s4=i;
						break;
					}
				}
			}
			if(s4-i==min(s1,s2)){
				for(int i=0;i<min(s1,s2);i++){
					if(s1<=s2){
						cout<<a1[i];
					}else{
						cout<<a2[i];
					}
				}
				cout<<" is substring of ";
				for(int i=0;i<max(s1,s2);i++){
					if(s1>=s2){
						cout<<a1[i];
					}else{
						cout<<a2[i];
					}
				}
				return 0;
			}
		}
	}
	cout<<"No substring";
	return 0;
}