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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;


namespace Atcoder
{
    class Program
    {

        static List<int[]> list = new List<int[]>();
        static int[] yMove = new int[] {-1,1,0,0};
        static int[] xMove = new int[] {0,0,-1,1};
        static bool[,] miz;

        static void Main(string[] args)
        {

            //var line1 = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            //var N = line1[0];
            //var M = line1[1];
            //var a = new long[M];
            //var b = new long[M];

            //int bridge = 0;

            //int[,] dag = new int[N,N];

            //for (int i = 0; i < M; i++)
            //{
            //    var line2 = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            //    a[i] = line2[0]-1;
            //    b[i] = line2[1]-1;
            //    dag[a[i], b[i]] = 1;
            //    dag[b[i], a[i]] = 1;
            //}

            //for (int i = 0; i < M; i++)
            //{
            //    bool[] visited = new bool[N];
            //    dag[a[i], b[i]] = 0;
            //    dag[b[i], a[i]] = 0;
            //    DFS(0,visited,dag);

            //    if (visited.Where(n => n == true).Count() != N)
            //    {
            //        bridge++;
            //    }

            //    dag[a[i], b[i]] = 1;
            //    dag[b[i], a[i]] = 1;
            //}
            //Console.WriteLine(bridge);
            //var line1 = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);

            //var A = line1[0];
            //var B = line1[1];
            //var C = line1[2];
            //var D = line1[3];
            //var E = line1[4];
            //var F = line1[5];

            //var N = int.Parse(Console.ReadLine());
            //char[] mozi = new char[N];
            //long[] MARCH = new long[5];
            //long cnt = 0;


            //for (int i = 0; i < N; i++)
            //{
            //    mozi[i] = Console.ReadLine().ToCharArray()[0];
            //}

            //MARCH[0] = mozi.Where(n => n == 'M').Count();
            //MARCH[1] = mozi.Where(n => n == 'A').Count();
            //MARCH[2] = mozi.Where(n => n == 'R').Count();
            //MARCH[3] = mozi.Where(n => n == 'C').Count();
            //MARCH[4] = mozi.Where(n => n == 'H').Count();

            //for (int i = 0; i < 3; i++)
            //{
            //    for (int j = i + 1; j < 4; j++)
            //    {
            //        for (int k = j + 1; k < 5; k++)
            //        {
            //            cnt += MARCH[i] * MARCH[j] * MARCH[k];
            //        }
            //    }
            //}

            //Console.WriteLine(cnt);

            //var N = int.Parse(Console.ReadLine());

            //var line1 = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            //var line2 = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            //int candy = 0;
            //int MAX = 0;

            //for (int i = 0; i < N; i++)
            //{
            //    for (int k = 0; k <= i; k++)
            //    {
            //        candy += line1[k];
            //    }

            //    for (int j = N - 1; j >= i; j--)
            //    {
            //        candy += line2[j];
            //    }

            //    MAX = Math.Max(candy,MAX);
            //    candy = 0;
            //}

            //Console.WriteLine(MAX);

            //var N = int.Parse(Console.ReadLine());
            //List<int[]> list = new List<int[]>();
            //int t = 0;
            //int x = 0;
            //int y = 0;

            //for (int i = 0; i < N; i++)
            //{
            //    var txy = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            //    list.Add(txy);
            //}

            //foreach (var item in list)
            //{
            //    if (item[0] - t >= Math.Abs(item[1] + item[2] - x - y))
            //    {

            //        if (((item[0] - t) % 2 == 1 && Math.Abs(x + y - item[1] - item[2]) % 2 == 1) ||
            //            ((item[0] - t) % 2 == 0 && Math.Abs(x + y - item[1] - item[2]) % 2 == 0))
            //        {
            //            t = item[0];
            //            x = item[1];
            //            y = item[2];
            //        }
            //        else
            //        {
            //            Console.WriteLine("No");
            //            return;
            //        }
            //    }
            //    else
            //    {
            //        Console.WriteLine("No");
            //        return;
            //    }
            //}

            //Console.WriteLine("Yes");

            //var line1 = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);

            //if (line1[1] >= 10000)
            //{
            //    for (int i = 0; i <= line1[1]/10000; i++)
            //    {
            //        for (int j = 0; j <= line1[1] / 5000; j++)
            //        {
            //            if (10000 * i + 5000 * j + (line1[0] - i - j) * 1000 == line1[1] && line1[0] - i - j >= 0)
            //            {
            //                Console.WriteLine("{0} {1} {2}",i,j,line1[0] - i - j);
            //                return;
            //            }
            //        }
            //    }
            //}
            //else
            //{
            //    for (int i = 0; i < 2; i++)
            //    {
            //        for (int j = 0; j <= 9; j++)
            //        {
            //            if (5000 * i + 1000 * j == line1[1] && i + j == line1[0])
            //            {
            //                Console.WriteLine("{0} {1} {2}", 0, i, j);
            //                return;
            //            }
            //        }
            //    }
            //}

            //Console.WriteLine("{0} {1} {2}", -1, -1, -1);


            //var N = int.Parse(Console.ReadLine());
            //int[,] station = new int[N,3];
            //long sum = 0;


            //for (int i = 0; i < N - 1; i++)
            //{
            //    var line = Array.ConvertAll(Console.ReadLine().Split(),int.Parse);
            //    station[i, 0] = line[0];
            //    station[i, 1] = line[1];
            //    station[i, 2] = line[2];
            //}

            //for (int j = 0; j < N -1; j++)
            //{
            //    for (int i = j; i < N - 1; i++)
            //    {
            //        var F = station[i, 2];
            //        var S = station[i, 1];
            //        if (i == j)
            //        {
            //            sum += station[i, 0] + station[i, 1];
            //        }
            //        else
            //        {
            //            if (sum < S)
            //            {
            //                sum = S + station[i, 0];
            //            }
            //            else if (sum % F == 0)
            //            {
            //                sum += station[i, 0];
            //            }
            //            else
            //            {
            //                sum += F - (sum % F) + station[i, 0];
            //            }
            //        }
            //    }

            //    Console.WriteLine(sum);
            //    sum = 0;
            //}
            //Console.WriteLine(sum);

            //var line = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            //long A = line[0];
            //int i = 0;

            //while (A <= line[1])
            //{
            //    A *=2;
            //    i++;
            //}

            //Console.WriteLine(i);
            //var N = long.Parse(Console.ReadLine());
            //var line = Array.ConvertAll(Console.ReadLine().Split(),long.Parse);
            //Dictionary<long, long> dic = new Dictionary<long, long>();
            //long sum = 0;

            //for (int i = 0; i < N; i++)
            //{
            //    if (dic.ContainsKey(line[i]))
            //    {
            //        dic[line[i]]++;
            //    }
            //    else
            //    {
            //        dic.Add(line[i], 1);
            //    }
            //}

            //foreach (var item in dic)
            //{
            //    if (item.Key == item.Value)
            //    {

            //    }
            //    else if (item.Key < item.Value)
            //    {
            //        sum += item.Value - item.Key;
            //    }
            //    else
            //    {
            //        sum += item.Value;
            //    }
            //}

            //Console.WriteLine(sum);

            //var line = Array.ConvertAll(Console.ReadLine().Split(),long.Parse);
            //var N = line[0];
            //var K = line[1];

            //var line2 = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            //long cnt = 0;
            //long sum = 0;

            //long[] lngarray = new long[N];

            //for (int i = 0; i < N; i++)
            //{
            //    lngarray[line2[i]-1]++;
            //}

            //if (lngarray.Where(n => n !=0).Count() <= K)
            //{
            //    Console.WriteLine(0);
            //    return;
            //}

            //var orderlng = lngarray.Where(n => n != 0).OrderBy(n => n).ToArray();

            //for (int i = 0; i < orderlng.Length; i++)
            //{
            //    if (cnt == orderlng.Length - K)
            //    {
            //        Console.WriteLine(sum);
            //        return;
            //    }
            //    else
            //    {
            //        sum += orderlng[i];
            //        cnt++;
            //    }
            //}
            //int soe = 0;
            //saiki(soe, new int[10]);

            //var N = int.Parse(Console.ReadLine());
            //var F = new List<int[]>();
            //var P = new List<int[]>();

            //for (int i = 0; i < N; i++)
            //{
            //    var line = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            //    F.Add(line);
            //}

            //for (int i = 0; i < N; i++)
            //{
            //    var line = Array.ConvertAll(Console.ReadLine().Split(), int.Parse);
            //    P.Add(line);
            //}

            //int sum = int.MinValue;
            //list.RemoveAt(0);
            //foreach (var item in list)
            //{
            //    int tmpsum = 0;
            //    for (int i = 0; i < N; i++)
            //    {
            //        int c = 0;
            //        for (int j = 0; j < 10; j++)
            //        {
            //            if (item[j] == 1 && F[i][j] == 1)
            //            {
            //                c++;
            //            }
            //        }

            //        tmpsum += P[i][c];
            //    }
            //    sum = Math.Max(sum, tmpsum);
            //}

            //Console.WriteLine(sum);


            //var line = Console.ReadLine().ToCharArray();
            //int[] hai = new int[7];

            //hai[0] = int.Parse(line[0].ToString());
            //hai[2] = int.Parse(line[1].ToString());
            //hai[4] = int.Parse(line[2].ToString());
            //hai[6] = int.Parse(line[3].ToString());

            //saikiseven(1,0, hai);

            //string ope1 = list[0][1] == 0 ? "+" : "-";
            //string ope2 = list[0][3] == 0 ? "+" : "-";
            //string ope3 = list[0][5] == 0 ? "+" : "-";

            //Console.WriteLine("{0}{1}{2}{3}{4}{5}{6}=7", list[0][0],ope1, list[0][2], ope2,list[0][4], ope3,list[0][6]);

            //var N = long.Parse(Console.ReadLine());
            //var line = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
            //long[] A = new long[N];

            //for (int i = 0; i < N; i++)
            //{
            //    A[i] = Math.Abs(i - (N - i -1));
            //}

            //var tmp1 = line.OrderBy(n => n).ToArray();
            //var tmp2 = A.OrderBy(n => n).ToArray();

            //for (int i = 0; i < N; i++)
            //{
            //    if (tmp1[i] != tmp2[i])
            //    {
            //        Console.WriteLine(0);
            //        return;
            //    }
            //}

            //long X = 1;

            //for (int i = 0; i < N/2; i++)
            //{
            //    X *= 2;
            //    X %= 1000000007;
            //}
            //Console.WriteLine(X);

            //var line =Array.ConvertAll(Console.ReadLine().Split(),int.Parse);

            //var sx = line[0];
            //var sy = line[1];
            //var tx = line[2];
            //var ty = line[3];

            //var path1 = new string('U', ty - sy) + new string('R',tx - sx);
            //var path2 = new string('D', ty - sy) + new string('L', tx - sx);
            //var path3 = new string('L', 1) + new string('U', ty - sy + 1) + new string('R', tx - sx + 1) + new string('D', 1);
            //var path4 = new string('R', 1) + new string('D', ty - sy + 1) + new string('L', tx - sx + 1) + new string('U', 1);
            //Console.WriteLine(path1 + path2 + path3 + path4);
            //int[] sosuu = new int[1000];

            //var N = int.Parse(Console.ReadLine());
            //int[] sosuu = new int[1001];

            //long ans = 1;

            //for (int i = 1; i < N + 1; i++)
            //{
            //    PrimeFactors(i, sosuu);
            //}

            //for (int i = 2; i < N + 1; i++)
            //{
            //    ans *= sosuu[i] + 1;
            //    ans %= 1000000007;

            //}

            //Console.WriteLine(ans);

            var N = long.Parse(Console.ReadLine());
            long X = 0;
            long Y = 0;

            X = N / 11;

            if (X == 0)
            {
                Y = 0;
            }
            else if ((N - (11 * X)) <= 6)
            {
                Y = 1;
            }
            else
            {
                Y = 2;
            }

            Console.WriteLine(X * 2 + Y);
        }

        public static void PrimeFactors(int n,int[] sosuu)
        {
            int i = 2;
            int tmp = n;

            while (i * i <= n) 
            {
                if (tmp % i == 0)
                {
                    tmp /= i;
                    sosuu[i]++;
                }
                else
                {
                    i++;
                }
            }
            if (tmp != 1) sosuu[tmp]++;
        }


        public static void DFSzahyo(int x, int y,int[] s,int[] g)
        {

            if (x == g[0] && y == g[1])
            {
                return;
            }
            miz[x, y] = true;
            for (int i = 0; i < 4; i++)
            {
                if (miz[x + xMove[i], y + yMove[i]] != true)
                {
                    DFSzahyo(x + xMove[i], y + yMove[i],s,g);
                }
            }
        }

        public static void saikiseven(int ope, int sum ,int[] hairetui)
        {
            if (ope == 1)
            {
                sum = hairetui[ope - 1];
            }

            if (ope == 7 && sum == 7)
            {
                int[] dummy = new int[ope];
                hairetui.CopyTo(dummy, 0);
                list.Add(dummy);
                return;
            }
            else if (ope == 7 && sum != 7)
            {
                return;
            }

            for (int i = 0; i < 2; i++)
            {
                if (i == 0)
                {
                    sum += hairetui[ope + 1];
                    hairetui[ope] = i;
                    saikiseven(ope + 2, sum, hairetui);
                    sum -= hairetui[ope + 1];
                }
                else
                {
                    sum -= hairetui[ope + 1];
                    hairetui[ope] = i;
                    saikiseven(ope + 2, sum, hairetui);
                }
            }

            return;
        }

        public static void saiki(int soezi,int[] hairetui)
        {
            if (soezi == 10)
            {
                int[] dummy = new int[soezi];
                 hairetui.CopyTo(dummy,0);
                list.Add(dummy);
                return;
            }

            for (int j = 0; j < 2; j++)
            {
                hairetui[soezi] = j;
                saiki(soezi+1, hairetui);
            }

            return;
        }

        public static void DFS(int v,bool[] visited,int[,] dag)
        {
            visited[v] = true;

            for (int i = 0; i < visited.Length; i++)
            {
                if (dag[v, i] == 0) continue;
                if (visited[i]) continue;
                DFS(i,visited,dag);
            }

        }

        public static long LowerBound<T>(T[] arr, long start, long end, T value, IComparer<T> comparer)
        {
            long low = start;
            long high = end;
            long mid;
            while (low < high)
            {
                mid = ((high - low) >> 1) + low;
                if (comparer.Compare(arr[mid], value) < 0)
                    low = mid + 1;
                else
                    high = mid;
            }
            return low;
        }

        //引数省略のオーバーロード
        public static long LowerBound<T>(T[] arr, T value) where T : IComparable
        {
            return LowerBound(arr, 0, arr.Length, value, Comparer<T>.Default);
        }
        public static long UpperBound<T>(T[] arr, long start, long end, T value, IComparer<T> comparer)
        {
            long low = start;
            long high = end;
            long mid;
            while (low < high)
            {
                mid = ((high - low) >> 1) + low;
                if (comparer.Compare(arr[mid], value) <= 0)
                    low = mid + 1;
                else
                    high = mid;
            }
            return low;
        }

        //引数省略のオーバーロード
        public static long UpperBound<T>(T[] arr, T value)
        {
            return UpperBound(arr, 0, arr.Length, value, Comparer<T>.Default);
        }
    }

    /// <summary>
    /// Get min cost between two points
    /// </summary>
    //public class Dijkstra
    //{
    //    private int maxIndex = -1;
    //    private const int INF = Int32.MaxValue;

    //    private int[,] _edgeArray;

    //    /// <summary>
    //    /// Dijkstra, get min cost between two points
    //    /// should not contain negatie cost path
    //    /// </summary>
    //    /// <param name="size">max index of vertices</param>
    //    public Dijkstra(int size)
    //    {
    //        maxIndex = size + 1;
    //        _edgeArray = new int[maxIndex, maxIndex];

    //        for (int i = 0; i < _edgeArray.GetLength(0); i++)
    //        {
    //            for (int j = 0; j < _edgeArray.GetLength(1); j++)
    //            {
    //                _edgeArray[i, j] = INF;
    //                if (i == j) _edgeArray[i, j] = 0;
    //            }
    //        }
    //    }

    //    // Add a path(no direction) with its cost
    //    public void AddPath(int s, int t, int cost)
    //    {
    //        _edgeArray[s, t] = Math.Min(_edgeArray[s, t], cost);
    //        _edgeArray[t, s] = _edgeArray[s, t];
    //    }

    //    //Get the min cost between s and t
    //    //return Int32.MaxValue if no path
    //    public int GetMinCost(int s, int t)
    //    {
    //        int[] cost = new int[maxIndex];
    //        for (int i = 0; i < cost.Length; i++) cost[i] = INF;
    //        cost[s] = 0;

    //        var priorityQueue = new PriorityQueue<ComparablePair<int, int>>(maxIndex);
    //        priorityQueue.Push(new ComparablePair<int, int>(0, s));

    //        while (priorityQueue.Count() > 0)
    //        {
    //            var costDestinationPair = priorityQueue.Pop();
    //            if (cost[costDestinationPair.Item2] < costDestinationPair.Item1) continue;

    //            for (int i = 0; i < maxIndex; i++)
    //            {
    //                int newCostToi = _edgeArray[costDestinationPair.Item2, i] == INF ? INF :
    //                    costDestinationPair.Item1 + _edgeArray[costDestinationPair.Item2, i];
    //                if (newCostToi < cost[i])
    //                {
    //                    cost[i] = newCostToi;
    //                    priorityQueue.Push(new ComparablePair<int, int>(newCostToi, i));
    //                }
    //            }
    //        }

    //        return cost[t];
    //    }
    //}

    //public class ComparablePair<T, U> : IComparable where T : IComparable<T>
    //{
    //    public readonly T Item1;
    //    public readonly U Item2;

    //    public int CompareTo(object obj)
    //    {
    //        ComparablePair<T, U> castedObj = (ComparablePair<T, U>)obj;
    //        return this.Item1.CompareTo(castedObj.Item1);
    //    }

    //    public ComparablePair(T t, U u)
    //    {
    //        Item1 = t;
    //        Item2 = u;
    //    }
    //}



}