Python提问:求质数和，为啥不对呢，求帮帮我

请问我这为啥不对啊，实在看不出来了，求大家帮帮我

n = int(input(">>>"))

sum = 0
for i in range(2, n + 1):
    flg = True
    for j in range(2, i):
        if i % j == 0:
            flg = False
            break
    if flg:sum += i    
print(sum)

a = int(input('输入a:'))
b = int(input('输入b:'))
sum = 0

for i in range(a, b+1):
k = 2
if i >= 2:
while i % k != 0:
k +=1
if i==k:
sum += i

print(sum)