#include<stdio.h>
#include<math.h>
int min(float score)
{
    if(score<0)
    {
        printf("Invalid Input\n");
        return -1;
    }
    return (int)ceil(score/3.0);
}
int main()
{
    float score;
    scanf("%f",&score);
    int result=min(scorel);
    if(result!=-1)
    {
        printf("%d",result);
    }
    return 0;
}