#include<iostream> #include<cstring> using namespace std; int main(){ char a[1001],b='0'; cin>>a; int c; c=strlen(a); for(int i=0;i<c;i++){ if(a[i]>='0'&&'9'>=a[i]&&a[i]>b) b=a[i]; } cout<<b; return 0; }