Программа не содержит статического метода "Main", подходящего для точки входа - C#

using System;
using System.Numerics;
 
namespace FFT
{
public class FFT
{
private static Complex w(int k, int N)
{
if (k % N == 0) return 1;
double arg = -2 * Math.PI * k / N;
return new Complex(Math.Cos(arg), Math.Sin(arg));
}
public static Complex[] fft(Complex[] x)
{
Complex[] X;
int N = x.Length;
if (N == 2)
{
X = new Complex[2];
X[0] = x[0] + x[1];
X[1] = x[0] - x[1];
}
else
{
Complex[] x_e = new Complex[N / 2];
Complex[] x_o = new Complex[N / 2];
for (int i = 0; i < N / 2; i++)
{
x_e[i] = x[2 * i];
x_o[i] = x[2 * i + 1];
}
Complex[] X_e = fft(x_even);
Complex[] X_o = fft(x_odd);
X = new Complex[N];
for (int i = 0; i < N / 2; i++)
{
X[i] = X_e[i] + w(i, N) * X_o[i];
X[i + N / 2] = X_e[i] - w(i, N) * X_o[i];
}
}
return X;
}
public static Complex[] nfft(Complex[] X)
{
int N = X.Length;
Complex[] X_n = new Complex[N];
for (int i = 0; i < N / 2; i++)
{
X_n[i] = X[N / 2 + i];
X_n[N / 2 + i] = X[i];
}
return X_n;
}
}
}