#include <fstream>

using namespace std;

int zero( int n ){
    int z=0;
    while ( n>=5 ){
   if ( n%5==0 )
    z++; n/=5;
   }
  return z;
}

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");

    long p; in>>p;

   if( p==0 ) out<<1;

      long sum=0;
   for(int i=5; i<=p; i+=5 )
    sum+=zero(i);
out<<sum;

    return 0;
}