import std.stdio;
import std.range;
import std.array;
import std.string;
import std.conv;
import std.typecons;
import std.algorithm;
import std.container;
import std.typecons;
import std.random;
import std.csv;
import std.regex;
import std.math;
import core.time;
import std.ascii;
import std.digest.sha;
import std.outbuffer;

void main() {
	long x = readln.chomp.to!long;
	long left = 0;
	long right = x + 1;
	while (right - left > 1) {
		long mid = (left + right) / 2;
		long five = mid / 2;
		long six = mid - five;
		if (five * 5 + six * 6 < x) {
			left = mid;
		} else {
			right = mid;
		}
	}
	right.writeln;
}

