#include<stdio.h>
int main(){
int units;
double bill=0.0;
if(scanf("%d",&units)!=1){
    printf("Invalid input\n");
    return 0;
    
}
if(units<0){
    printf("Invalid input\n");
    return 0;
}
if(units<=100){
    bill=units*0.50;
}else if (unit<=200){
    bill=100*0.50+100*0.15;
}else{
    bill=100*0.50+100*0.15+(units-200*0.20);
}
printf("%.2lf\n",bill);
return 0;
}