#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+=;
        }
        printf("%d\n",turns);
    }
    return 0;
}