#include<stdio.h>
int main(){
    float score_f;
    printf(" ");
    scanf("%f", &score_f);
    if(score_f < 0){
        printf("Invalid input\n");
        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;
}