Buggy python submission (verdict: Runtime Error):
n = int(input())

for _ in range(n):
  m, f, r = map(int, input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 && s < 80:
    print("B")
elif s >= 50 && s < 65 || f >= 50:
    print("C")
elif s >= 30 && s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")



Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
n = int(input())

for _ in range(n):
  m, f, r = map(int, input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 and s < 80:
    print("B")
elif (s >= 50 and s < 65) or f >= 50:
    print("C")
elif s >= 30 and s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")



Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
n = int(input())

for _ in range(n):
  m, f, r = map(int,input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 and s < 80:
    print("B")
elif (s >= 50 and s < 65) or f >= 50:
    print("C")
elif s >= 30 and s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")



Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
n = int(input())

for _ in range(n):
  m,f,r = map(int,input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 and s < 80:
    print("B")
elif (s >= 50 and s < 65) or f >= 50:
    print("C")
elif s >= 30 and s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")



Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
n=int(input())
for _ in range(n):
  m,f,r = map(int,input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 and s < 80:
    print("B")
elif (s >= 50 and s < 65) or f >= 50:
    print("C")
elif s >= 30 and s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")



Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
n = int(input())

for _ in range(n):
  m, f, r = map(int, input().split())
  s = m+f

if s >= 80:
    print("A")
elif s >= 65 and s < 80:
    print("B")
elif (s >= 50 and s < 65) or f >= 50:
    print("C")
elif s >= 30 and s < 50:
    print("D")
else:
    print("F")


if m == f == r== -1:
    print("F")


Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")

Buggy python submission (verdict: Runtime Error):
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    
    if s >= 80:
        print("A")
    elif s >= 65 and s < 80:
        print("B")
    elif (s >= 50 and s < 65) or f >= 50:
        print("C")
    elif s >= 30 and s < 50:
        print("D")
    else:
        print("F")
    




Fixed submission:
while True:
    m, f, r = map(int, input().split())
    if m == f == r== -1:
        break
    s = m + f
    if m == -1 or f == -1:
        print("F")
    elif s >= 80:
        print("A")
    elif s >= 65:
        print("B")
    elif s >= 50:
        print("C")
    elif s >= 30:
        if r >= 50:
            print("C")
        else:
            print("D")
    else:
        print("F")