Code Chef: Code Not Correct? Unexpected Behaviour - c++

Question

Recently I've started doing Code Chef challenges to practice programming in C and C++ when I came across the ATM challenge. The challenge (which I expected to be relatively easy) was to create a program that withdraws money from a bank account if the withdrawal amount is a multiple of 5 and if the withdraw > balance. If the transaction is accepted it also charges a fee of 0.5, else it just reprints the bank data.
The link to the challenge is here:
https://www.codechef.com/problems/HS08TEST
The program runs perfectly fine for me on my computer but for some reason it is wrong.
Here is my program:
#include <iostream>
#include <cstdio>
#include <iomanip>
using std::cout; using std::cin; using std::endl;
class Bank_data {
private:
double balance;
public:
void withdraw (int amount) {
if (amount > balance - 0.5 || amount % 5 != 0)
printf("%.2f\n", balance);
else
printf("%.2f\n", balance - amount - 0.5);
}
void setBalance (int amount) {
balance = amount;
}
};
int main () {
Bank_data bd;
int withdraw, init_val;
cin >> std::fixed;
cin >> std::setprecision(2) >> withdraw >> init_val;
bd.setBalance (init_val);
bd.withdraw (withdraw);
return 0;
}
Sample io:
I: 5 500
O1: 494.50
I2: 600 500
O2: 500.00
I3: 4 500
O3: 500.00