#include<stdio.h>
intmain(){
    float score_f;
    printf(" ");
    scanf("%f", &score_f);
    if (score_f < 0){
        printf("Invalid Input\n");
    } else{
        int score_i = (int)score_f;
        int turns = (score_i + 2) / 3;
        printf("%d\n", turns);
    }
    return 0;
}