#include <fstream>

using namespace std;

inline unsigned long long int find_five(long p) {
     unsigned long i=0,zero=0,j;
     while(p) {
          i+=5;
          j=i/5;
          zero++;
          p--;
          verifica:
          if(j%5==0) {
               zero++;
               p--;
               j/=5;
               goto verifica;
          }
     }
     return i;
}

int main() {
     long p;
     ifstream f("fact.in");
     f>>p;
     f.close();
     ofstream g("fact.out");
     g<<find_five(p);
     g.close();
     return 0;
}