#include<stdio.h>
#include<math.h>
{
    int minTurns(float score)
    {
        int s=(int)round(score);
        if(s<0)return-1;
        return(s+2)/3;
    }
    
int main()
{
    float score;
    scanf("%f",&score);
    int turns=minTurns(score);
    if(turns==-1)
    {
        printf("Invalid score\n");
    }
    else
    {
        printf("Minimum turns:%d\n",turns);
    }
    return 0;
}