#include<stdio.h>
#include<math.h>
int mturns(int score)
{
    if (score<-1)
    {
        return -1;
    }
    int turn=0;
    while (score>0)
    {
        if (score>=3)
           score -=3;
           else if(score==2)
           score -=2;
           else
           score -=1;
           turn++;
    }
           return turns;
}
int main ()
{
    int score;
    scanf("%d",&score);
    int result =mturns(score);
    if (result==-1)
    printf("Invalid Input\n");
    else
    printf("%d\n",result);
    return 0;
}