a,b,c,d=map(int,input().split())
if (((3*((d**2)-(c**2)))/(a*b)/10))>=0:
print('%.2f'%((3*((d**2)-(c**2)))/(a*b)/10))
else:
print('Error')
a,b,c,d=map(int,input().split())
if (((3*((d**2)-(c**2)))/(a*b)/10))>=0:
print('%.2f'%((3*((d**2)-(c**2)))/(a*b)/10))
else:
print('Error')
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