sun=0
start=1
while True:
    start1=start%2
    if start1==1:
        sun = start + sun
    elif start1==0:
        sun=sun-start
    if start==100:
        break
    start += 1
print(sun)

 1 sun=0
 2 start=1
 3 while True:
 4     start1=start%2
 5     if start1==1:
 6         sun = start + sun
 7     elif start1==0:
 8         sun=sun-start
 9     if start==100:
10         break
11     start += 1
12 print(sun)

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