function searchLeft( x, k, r, p ) {
	while ( true ) {
		if ( x === 0 || cdf( x - 1.0, r, p ) < k ) {
			return x;
		}
		x -= 1;
	}
}
Performs a search to the left.

@param {NonNegativeInteger} x - starting guess
@param {Probability} k - probability
@param {PositiveNumber} r - number of failures until experiment is stopped
@param {Probability} p - success probability
@returns {NonNegativeInteger} `k` quantile of the specified distribution