use proconio::input;

fn main() {
    input! {
        n: i64
    }
    let mut low = 0;
    let mut high = 100_000_000_000_000_000_i64;
    while high - low > 1 {
        let mid = (high + low) / 2;
        if check(mid) < n {
            low = mid;
        } else {
            high = mid;
        }
    }
    println!("{}", high);
}

fn check(mid: i64) -> i64 {
    if mid <= 2 {
        mid
    } else {
        (mid - 3) / 5 + 3
    }
}