def recurse(x, y, ans):
if x == y:
ans += 1
elif x > y:
if y == 1:
ans += x
else:
ans += 1
x = x-y
recurse(x, y, ans)
elif x < y:
if x == 1:
ans += y
else:
ans += 1
y = y-x
recurse(x, y, ans)
return ans
p = int(input())
q = int(input())
r = int(input())
s = int(input())
ans = 0
a = 0
for i in range(p, q+1):
for j in range(r, s+1):
x = max(i,j)
y = min(i,j)
a += recurse(x, y)
print(a)
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