#include <stdio.h>
int main(){
    float score:
    scanf("%f",&score);
    if (score < 0){
        print("invalid input");
        return 0;
    }
    int s = (int)score;
    int turns =s/ 3;
    
    if(s % 3 !=0){
        turn += 1;
    }
    printf("%d",turns);
    return  0;
}