Buggy python submission (verdict: Runtime Error):
(m, f, r) = [int(i) for i in input().split()]
    if m==-1 and f==-1 and r==-1:
        break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g >= 80:
        print('A')
    elif g >= 65:
        print('B')
    elif g >= 30 or r >= 50:
        print('C')
    else:
        print('D')
~                    

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
        if m==-1 and f==-1 and r==-1:
            break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g >= 80:
        print('A')
    elif g >= 65:
        print('B')
    elif g >= 50 or r >= 50:
        print('C')
    else:
        print('D')
~                   

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
        if m==-1 and f==-1 and r==-1:
            break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g < 50 or r < 50:
        print('D')
    elif g < 65:
        print('C')
    elif g < 80:
        print('B')
    else:
        print('A')

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
        if m == f == r == -1:
            break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g < 50 or r < 50:
        print('D')
    elif g < 65:
        print('C')
    elif g < 80:
        print('B')
    else:
        print('A')

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
        if m==f==r==-1:
            break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g < 50 and r < 50:
        print('D')
    elif g < 65:
        print('C')
    elif g < 80:
        print('B')
    else:
        print('A')
~                    

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m==f==r==-1:
        break

    g = m + f
    if m == -1 or f == -1 or g < 30:
        print('F')
    elif g < 50 and r < 50:
        print('D')
    elif g < 65:
        print('C')
    elif g < 80:
        print('B')
    else:
        print('A')
~                    

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')

Buggy python submission (verdict: Runtime Error):
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')
~                 

Fixed submission:
while True:
    (m, f, r) = [int(i) for i in input().split()]
    if m == f == r == -1:
        break
 
    total = m + f
    if m == -1 or f == -1 or total < 30:
        print('F')
    elif total < 50 and r < 50:
        print('D')
    elif total < 65:
        print('C')
    elif total < 80:
        print('B')
    else:
        print('A')