#include<iostream>
#include<fstream>
using namespace std;

int CateZerouri(int n) {
	int k = 5, s = 0;
	while (n / k != 0) {
		s += n / k;
		k *= 5;
	}
	return s;
}

int main() {
	int p, n;
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	fin >> p;
	n = 5 * p;
	while (CateZerouri(n) >= p) {
		n--;
	}
	fout << n+1;
	fin.close();
	fout.close();

	return 0;
}