#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 remiander=intscore%3;
        if(remainder!=0)
        {
            turns+=1;
        }
        printf("%d",turns);
    }
    return 0;
}