#include <stdio.h>
int main(){
float amount;
float result;
if (scanf("%f",&amount)!=0){
if (amount>15.0){
result = 2.5*amount-17.5;
printf("%.2f",result);
}else{
result = 4*amount/3.0;
printf("%.2f",result);
}
}else{
printf("输入数据存在错误");
}
return 0;
}
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