#include<iostream>
#include<fstream>
#include<iomanip>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int p,s;
long long n,x[100]={5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625};
int main()
{
	int i=1;
	f>>p;
	n=max(p*5,1);
	for(i=1;i<=11&&n>=x[i];i++)
	{
		n-=5*i;
	}
	g<<n;
	return 0;
}