An interview question: About Probability

An interview question:

Given a function f(x) that 1/4 times returns 0, 3/4 times returns 1. Write a function g(x) using f(x) that 1/2 times returns 0, 1/2 times returns 1.

My implementation is:

function g(x) = {
    if (f(x) == 0){ // 1/4 
        var s = f(x) 
        if( s == 1) {// 3/4 * 1/4
            return s  //   3/16
        } else {
            g(x)
        } 
    } else { // 3/4
            var k = f(x)
            if( k == 0) {// 1/4 * 3/4
                return k // 3/16 
            }  else {
                g(x)
            }       
    }
}

Am I right? What's your solution?(you can use any language)