SmallR is an archer. SmallR is taking a match of archer with Zanoes. They try to shoot in the target in turns, and SmallR shoots first. The probability of shooting the target each time is <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/a7487d7e62f90136b78ae3fbf0a008396f146e13.png" style="max-width: 100.0%;max-height: 100.0%;"/> for SmallR while <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/c443c7703e51f03d0eece0b96b9e84e425878209.png" style="max-width: 100.0%;max-height: 100.0%;"/> for Zanoes. The one who shoots in the target first should be the winner.

Output the probability that SmallR will win the match.
A single line contains four integers <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/488158367221f441ba94b9475c03436069df2a7e.png" style="max-width: 100.0%;max-height: 100.0%;"/>.
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#       ||      //      \\      ||     || //   ||
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#  code

def solve():
    a,b,c,d = map(int, input().split())

    p = a / b
    q = c / d

    ans = p * (1  / (1 - (1 - p) * (1 - q)))
    print(ans)
    return

def main():
    t = 1
    # t = int(input())
    for _ in range(t):
        solve()

if __name__ == "__main__":
    main()