# Arup Guha
# 3/17/2025
# Solution to 2025 HSPT Problem: Meet in the Middle

# Get input
xpos = [int(x) for x in input().split()]
vel = [int(x) for x in input().split()]

# Ta da!
# Total distance is the difference of x's.
# Effective speed together is sum of speeds.
print( (xpos[1]-xpos[0])/(vel[0]+vel[1]) )