#include<fstream.h>
#define input "fact.in"
#define output "fact.out"



int main()
	{
	long h,x;
	int n,k,gr=0;
	ifstream fin(input);
	ofstream fout(output);
	fin>>n;
	x=n;
	h=1;
	while(h*5+1<n)
		{
		h=(h*5)+1;
		gr++;
		}
	while(gr>0)
		{
		x-=(n/h);
		gr--;
		h--;
		h=h/5;
		}
	fout<<x*5;
	return 0;
	}