计算1-2+3-4+5.。。。。99的结果

#计算1-2+3-4+5-6+7。。。。。。。99的结果
count = 1
sum = 0
while count < 100:
    if count%2 == 0:
        sum = sum-count
    else:
        sum = sum + count
    count += 1
print(sum)