#include <fstream>
#include <iostream>

using namespace std;

int main()
{
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    long long p,i,x;
    fin>>p;
     if(p==1)
      cout<<0;
     else
     {
      for(i=5;p!=0;i+=5)
      { x=i;
       while(x%5==0)
        {p--;x=x/5;}
      }
     fout<<i-5;
     }
    return 0;
}