#include <iostream>

using namespace std;

int main() {
    long long n,c,maxx=0;
    cin >> n;
        while(n!=0)
        {
            c=n%10;
            n/=10;
            if(c%2==1 && c>maxx)
                maxx=c;
        }
        if(maxx==0){
            cout<<"nu exista";
        }else
        cout<<maxx;
    return 0;
}