#include<stdio.h>
int main()
{
    int units;
    scanf("%d",&units);
    
    if(units < 0)
    {
        printf("Invalid input");
    }
    else
    {
        float bill 0.0;
        if(units <= 100)
        {
            bill = units*0.10;
        }
        else if(units <= 200)
        {
            bill = (100*0.10) + ((units-100)*0.15);
        }
        else
        {
            bill = (100*0.10) + (100*0.15) + ((units - 200)*0.20);
        }
        printf("%.2f\n",bill);
    }
    return 0;
}