Problem:
Score : 300 points

Problem Statement

Snuke has decided to play with a six-sided die. Each of its six sides shows an integer 1 through 6, and two numbers on opposite sides always add up to 7.

Snuke will first put the die on the table with an arbitrary side facing upward, then repeatedly perform the following operation:

Operation: Rotate the die 90° toward one of the following directions: left, right, front (the die will come closer) and back (the die will go farther). Then, obtain y points where y is the number written in the side facing upward.

For example, let us consider the situation where the side showing 1 faces upward, the near side shows 5 and the right side shows 4, as illustrated in the figure.
If the die is rotated toward the right as shown in the figure, the side showing 3 will face upward.
Besides, the side showing 4 will face upward if the die is rotated toward the left, the side showing 2 will face upward if the die is rotated toward the front, and the side showing 5 will face upward if the die is rotated toward the back.

Find the minimum number of operation Snuke needs to perform in order to score at least x points in total.

Constraints

1 ≦ x ≦ 10^{15}

x is an integer.

Input

The input is given from Standard Input in the following format:

x

Output

Print the answer.

Sample Input 1

7

Sample Output 1

2

Sample Input 2

149696127901

Sample Output 2

27217477801

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::*;
use std::str::FromStr;
use std::collections::HashMap;
use std::collections::BTreeMap;
use std::collections::BTreeSet;
use std::collections::HashSet;
use std::cmp;
use std::f64::consts;
use std::cmp::Ordering;
use std::collections::VecDeque; //push_back, pop_front

fn main() {
    let n: i64 = read();
    let mut ans = n/11*2;

    if n<=6{
        ans = 1;
    } else if n < 11 {
        ans +=2;
    } else if n % 11 != 0 {
        if n % 11 <= 6 {
            ans += 1;
        } else {
            ans +=2;
        }
    }
    println!("{}", ans);
}

// 素因数分解
fn prime_factorization(number: u64) -> Vec<u64> {
    let mut result = number;
    for i in 2..((number as f64).sqrt() as u64)+1 {
        if number % i == 0 {
            result = i;
            break;
        }
    }

    if result == number {
        return vec![number];
    } else {
        let mut v1 = vec![result];
        let mut v2 = prime_factorization(number / result);

        v1.append(&mut v2);

        return v1;
    }
}

fn calc_distance(xa: f64, ya: f64, xb: f64, yb: f64)->f64 {
    (f64::powf(xb-xa, 2.0) + f64::powf(yb-ya, 2.0)).sqrt()
}

fn calc_triangle_area(x1: f64, y1: f64, x2: f64, y2: f64, x3: f64, y3: f64) -> f64 {
    1.0/2.0 * ((x1-x3)*(y2-y3)-(x2-x3)*(y1-y3)).abs()
}

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

// 最大公約数
fn gcd(a: i64, b: i64) -> i64 {
    match b {
        0 => a,
        _ => gcd(b, a % b)
    }
}

// 最小公倍数
fn lcm(a: i64, b: i64) -> i64 {
    let g = gcd(a ,b);
    a / g * b
}

// 階乗-dp (overflow回避で1000000007の余りを使って計算)
fn kaijou_dp(n: i64) -> i64 {
    let mut dp: Vec<i64> = vec![0; n as usize+1];
    dp[0] = 1;
    dp[1] = 1;

    for i in 1..n {
        dp[i as usize+1] = dp[i as usize] % 1000000007 * (i+1)  % 1000000007;
    }
    return dp[n as usize];
}

// 階乗
fn kaijou(n: i64)->i64 {
    if n == 1 {
        return n;
    }
    return n * kaijou(n-1);
}

// 順列全列挙
pub trait LexicalPermutation {
    /// Return `true` if the slice was permuted, `false` if it is already
    /// at the last ordered permutation.
    fn next_permutation(&mut self) -> bool;
}

impl<T> LexicalPermutation for [T] where T: Ord {
    /// Original author in Rust: Thomas Backman <serenity@exscape.org>
    /// let mut data = [1, 2, 3];
    //    let mut permutations = Vec::new();
    //
    //    loop {
    //        permutations.push(data.to_vec());
    //        if !data.next_permutation() {
    //            break;
    //        }
    //    }
    //
    //    println!("{:?}", permutations);
    //    // [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
    fn next_permutation(&mut self) -> bool {
        // These cases only have 1 permutation each, so we can't do anything.
        if self.len() < 2 { return false; }

        // Step 1: Identify the longest, rightmost weakly decreasing part of the vector
        let mut i = self.len() - 1;
        while i > 0 && self[i-1] >= self[i] {
            i -= 1;
        }

        // If that is the entire vector, this is the last-ordered permutation.
        if i == 0 {
            return false;
        }

        // Step 2: Find the rightmost element larger than the pivot (i-1)
        let mut j = self.len() - 1;
        while j >= i && self[j] <= self[i-1]  {
            j -= 1;
        }

        // Step 3: Swap that element with the pivot
        self.swap(j, i-1);

        // Step 4: Reverse the (previously) weakly decreasing part
        self[i..].reverse();

        true
    }
}

//iより小さい数字の数 = lower_bound(&a, i) as i64;
//iより大きい数字の数 = n - upper_bound(&c, i) as i64;
fn lower_bound<T: Ord>(vec: &Vec<T>, x: T) -> usize {
    let (mut left, mut right): (i64, i64) = (-1, vec.len() as i64);

    while (right - left) > 1 {
        let mid = (right + left) / 2;

        if x <= vec[mid as usize] {
            right = mid;
        } else {
            left = mid;
        }
    }

    return right as usize;
}

fn upper_bound<T: Ord>(vec: &Vec<T>, x: T) -> usize {
    let (mut left, mut right): (i64, i64) = (-1, vec.len() as i64);

    while (right - left) > 1 {
        let mid = (right + left) / 2;

        if x < vec[mid as usize] {
            right = mid;
        } else {
            left = mid;
        }
    }

    return right as usize;
}