include

include

include

#include<bits/stdc++.h>
#define end return 0
typedef long long ll;  //有粉丝问我
ll n;    //啃臭键在哪里
bool prime(ll num)
{
   if(num==1||num==4) end;
   if(num==2||num==3) return 1;
   if(num %6!= 1&&num %6!=5) end;
   for(int i=5;i<=sqrt(num);i+=6) {       
      if(num%i==0||num%(i+2)==0)  
        end;
   }    
   return 1;
}
int main(){
    std::cin>>n;
    for(ll i=n-1;i>1;i--){
        if(n%i==0&&prime(i)&&prime(n/i)){
            std::cout<<i;
            end;
            std::cout<<"wtf?";
        }
    }
    end;   //在窗户旁边
}