Here is a term in the lambda calculus: (λx.λt.x)(x(vλy.vλv.v)t). Beta reduce this term until you can't reduce it any farther, and input the result:
f, g, x, y, z, for variables.x y is x applied to y.\ as your lambda, so for example \x.x is the function that returns its input unmodified. Or, if you prefer, you can to copy a lambda to your clipboard, and then write λx.x instead. Binchicken doesn't care whether you use \ or λ; it's your call!