#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 !=0)
        {
            turns +=1;
        }
        printf("%d", turns):
    }
    return 0;
}