using System;

​

static int[] Mystery(int[] X)

{

    int n = X.Length;

    int[] S = new int[n]; 

    S[0] = X[0];

​

    for (int i = 1; i < n; i++)

    {

        S[i] = X[i] + S[i-1];

    }

​

    return S;

}

​

int[] a = new int[] { 12, 2, 4};

int[] b = new int[] { 1, 3, 5, 7, 9 };

Console.WriteLine(String.Join(" ", a) + " >> " + String.Join(" ", Mystery(a)));

Console.WriteLine(String.Join(" ", b) + " >> " + String.Join(" ", Mystery(b)));