#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

const int N_MAX = 400000014;

int nr_zero(int n) {
	int p = 5, cnt = 0;
	while(p <= n){
		cnt += n / p;
		p *= 5;
	}
	return cnt;
}

int main() {
	int p;
	fin >> p;

	int b = 0, e = N_MAX, mid;//[b;e)
	while(e - b > 1){
		mid = (b + e) >> 1;
		if(nr_zero(mid) < p)
			b = mid;
		else
			e = mid;
	}

	fout << b + 1 << '\n';

	fin.close();
	fout.close();
	return 0;
}