#include <bits/stdc++.h>
using namespace std;

const string file_name = "fact";
ifstream fin(file_name + ".in");
ofstream fout(file_name + ".out");


int main(){

	int n, p = 5, s = 0, k, r = 0;
	fin >> k;
	if(k == 0)
		r = 1;
	for(int i = 1; true; i++){
		n = i;
		s = 0; p = 5;
		while(p <= n){
			s += n/p;
			p *= 5;
		}
		if(s < k){
			r = i + 1;
		}
		else
			break;
	}
	fout << r;

	return 0;

}