C++ вычислить сумму n слагаемых cosx - cosx^2 + cosx^3 + cosx^4 - cosx^5 + cosx^6 + cosx^7 - cosx^8 +

#include <iostream>
#include <cmath>
using namespace std;
void main(){
double result ;
int x,n=0,k = 2;
cin >> x >> n;
result = cos(pow(x, 1));
for (int i = 2;i<=n;++i)
{
if (i != k)
result += cos(pow(x, i));
else
{
result -= cos(pow(x, i));
k += 3;
}
}
cout << "result = " << result;
system("pause");
}