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