Help remembering a Putnam Problem [duplicate]

I recall that there was a Putnam problem which went something like this:

Find all real functions satisfying

$$f(s^2+f(t)) = t+f(s)^2$$

for all $s,t \in \mathbb{R}$.

There was a cool trick to solving it that I wanted to remember. But I don't know which test it was from and google isn't much help for searching with equations.

Does anyone know which problem I am thinking of so I can look up that trick?

It was problem 2 in the International Mathematical Olympiad in 1992 (Russia).

You may read several solutions here.

1971 A2 was "Determine all polynomials $P(x)$ such that $P(x^2+1)=(P(x))^2+1$ and $P(0)=0$."

No idea. But I have a book called Putnam and Beyond by Gelca and Andreescu, and on page 185 they present a problem from a book called Functional Equations: A Problem Solving Approach by B. J. Venkatachala, from Prism Books PVT Ltd., 2002. I think the Ltd. means the publisher is British.

Almost, the publisher is (or was?) in India (Bangalore):

http://www.prismbooks.com/

http://www.hindbook.com/order_info.php

EDIT, December 3, 2011: The book is available, at least, from an online firm in India that is similar to Amazon.com

http://www.flipkart.com/m/books/8172862652

on

http://www.flipkart.com/

I cannot tell whether they ship outside India. But it does suggest that contacting the publisher by email is likely to work.