#include<fstream>
using namespace std;
ifstream in ("factorial.in");
ofstream out ("factorial.out");
int main (){
    int n=0,n1,i=0,p;
    in>>p;
    while(i<p){
        n+=5;
        n1=n;
        while(n1>0){
            if(n1%5==0){
            i++;
            n1=n1/5;
            }
            else
            break;
        }
    }
out<<n;
return 0;
}