itsa基 24 計算複利

#include<iostream>
using namespace std;

int main()
{
long double r, sum;
long int n, p;
cin >> r;
cin >> n;
cin >> p;

sum = 0;
while (n > 0)
{
sum += p;
sum *= (1.0 + r);
n--;
}
cout << (long long)sum << endl;
return 0;
}