#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;
}