// editor1
#include<stdio.h>
#include<math.h>
    int min_turn(float score)
    {
        if(score<0)
        {
            printf("Invalid input\n");
            return -1;
        }
        return (int)ceil(score/3.0);
        {
            int main()
            {
                float score;
                scanf("%f",&score);
                int result=min_turn(score);
                if(result=-1)
            {
                printf("%d",result);
            }
            return 0;
        }