// editor1
#include<stdio.h>
#include<math.h>

int min turn(float score) {
    if (scors < 0) {
        printf("Invalid Input\n"),
        return -1;
    }
    return (int)cell(score/3);
}
 int main()
 {
     float score;
     scanf("%f", &score);
    int turns = min_turn(score);
    if (turns != -1) {
        printf("%d\n",turns);
    }
    return 0;
 }