// editor1
#include<stdio.h>
#include<math.h>
     int main_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;
     }