def bmi():
    """
        获取输入计算用户的BMI值
        BMI = kg/m^2
    """
    bmi_int = eval(input("输入身高(cm)： "))
    bmi_int = eval(input("请输入体重(kg): ")) / (bmi_int*bmi_int/10000)
    bmi_gj = {18.5: '国际偏瘦', 25: '国际正常', 30: '国际偏胖', 29: '肥胖'}    
    bmi_zg = {18.5: "国内", 24: "国内正常", 28: "国内偏肥", 27: "国内肥胖"}
    
    for i in bmi_gj:
        if bmi_int < i:
            gj = i
            break
        elif i == 29:
            gj = i
            
    for i in bmi_zg:
        if bmi_int < i:
            zg = i
            break
        elif i == 27:
            zg = i
    
    print('BMI数值为: {:.3f}'.format(bmi_int))
    print('BMI指标为:{} {}'.format(bmi_gj[gj], bmi_zg[zg]))

    return bmi_int, bmi_gj[gj]


def intjjh(n):
    '''
    计算 1-2+3-4...n 的和
    '''
    sums = 0
    for i in range(n+1):
        if i % 2 != 0:
            sums = sums + i
        else:
            sums = sums - i
    
    return sums

    
print(intjjh(966))