#include<bits/stdc++.h>
using namespace std;
string s;
char maxx='0'; 
int main(){
	cin>>s;
	for(int i=0;i<s.size();i++){
		if(int (s[i])%2==0&&int (s[i])>int(maxx)){
			maxx=s[i];
		}
	}
	if(maxx=='0'){
		cout<<"No";
	}
	else{
		cout<<maxx;
	}
    return 0;
}