#include<iostream>
using namespace std;
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	int c2=0,c5=0,i,n,x;

	cin>>n;

	for(i=1;i<=n;i++)
	{   
		int aux = i;
		while(aux%5==0) {c5=c5+1; 
		                 aux/=5;} // aux=aux/5;
	

	}
	            
	               
	cout<<c5;
	  


	return 0;         
}