/**
 * @param {number} N
 * @return {number}
 */
var fib = function(N) {
    
    var hash={};
    
    function fibon(number)
    {
        if(hash.hasOwnProperty(number))
        {
            return hash[number];
        }
        var result;
        if(number < 2 && number >=0)
        {
           result=number;
            
        }
        else
        {
            result=fibon(number-1)+fibon(number-2);
        }
        hash[number]=result;
        return result;
    }
    fibon(N);
};