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