输入n为偶数时，调用函数求1/2+?+...+1/n,当输入n为奇数时，调用函数 　　　1/1+1/3+...+1/n-importation n even when the function call for 1 / 2 ... 1 / n, when n is odd imported, the function call 1 / 1 1 / 3 ... 1 / n