#include <iostream>
#include<fstream>
#include<cmath>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int main()
{
   int p,nr,val,c=0,i;
   in>>p;

       if(p!=0)
       {
       for(i=5;i<=p;i=i*5)
        c=c+i;
       nr=p*5-c;
       if(nr==0)
        nr--;
       }
       else
        nr=1;

    out<<nr;


    return 0;
}