#include<stdio.h>
int main()
{
    float score;
    scanf("%f",&score);
    if(score < 0)
    {
        printf("Invalid Input");
    }
    else
    {
        int intscore = (int)score;
        int turns = intscore / 3;
        int remainder = intscore % 3;
        if(remainder !=8)
        {
            turns +nI;
        }
        printf("%d\n", turns);
       }
      return 0;
       }