计算1+3！+5！+7！+9！之和（利用循环结构，和用S表示，结果用？输出）用c#写代码

public int GetSum(int one,int two) {
int s = 0;
for (int i = one; i <= two; i+2)
s += i;
return s;
}

class MathClass
{
public int GetNum(int i) {
int s = 1;
while (i > 1)
s *= i--;
return s;
}

public int GetSum(int lastNum) {
int s = 0;
for (int i = 1; i <= lastNum; i = i + 2)
s += GetNum(i);
return s;
}
}

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这里调用:
MathClass x = new MathClass();
Console.Write(x.GetSum(9));