#include <fstream>

using namespace std;

#define nZero(n) ((int)n/5+(int)n/25)

ifstream f("fact.in");
ofstream g("fact.out");

int p;

int solve(int left, int right)
{
	if(left > right)
		return -1;

	int mid = (left+right)/2;
	
	int rez = nZero(mid);
	if(rez == p)
		return mid;

	if(rez > p)
		solve(left, mid-1);
	else
		solve(mid+1, right);
}

int main()
{
	f >> p;
	g << solve(1, 40);
}