'use strict';
  
  var exp = Math.exp;
  
  module.exports = function (x) {
  	if (isNaN(x)) return NaN;
  	x = Number(x);
  	if (x === 0) return 1;
  	if (!isFinite(x)) return Infinity;
  	return (exp(x) + exp(-x)) / 2;
  };