function evalRpn(input) {
    var outputStack = [];
    var rpnQueue = toRPolish(input);  
    while (rpnQueue.length > 0) {
        var cur = rpnQueue.shift();

        if (!isOperatorR(cur)) {
            outputStack.push(cur);
        } else {
            if (outputStack.length < 2) {
                throw "unvalid stack length";
            }
            var sec = outputStack.pop();
            var fir = outputStack.pop();

            outputStack.push(getResult(fir, sec, cur));
        }
    }

    if (outputStack.length != 1) {
        throw "unvalid expression";
    } else {
        return outputStack[0];
    }
}

function getResult(fir, sec, cur) {
    var s = fir + cur + sec;
    var r = eval(s);
    if (r < 0) {
        r = r * -1;
    }
    return r;
}

function isOperatorR(value) {
    var operatorString = "+-*/";
    return operatorString.indexOf(value) > -1
}

function isOperatorF(value) {
    var operatorString = "(){}[]";
    return operatorString.indexOf(value) > -1
}

function toRPolish(input) {
    var regex = /(\+|\-|\*|\/)+/;
    var array = input.replaceAll('\\(', '').replaceAll('\\)', '').replaceAll('\\{', '').replaceAll('\\}', '').replaceAll('\\[', '').replaceAll('\\]', '').split(regex);
    var RPolish = ""
    var isI = false;
    num = 0;
    var SymbolArray = new Array(100);
    var SymbolNum = -1;
    for (j = 0; j < input.length; j++) {
        if (input.charAt(j).match(/\d/)) {
            if (isI == false) {
                if (RPolish.length > 0) {
                    RPolish += ','
                }
                RPolish += array[num];
                num++;
                isI = true;
            }
        }
        else {
            var c = input.charAt(j);
            if (isOperatorR(c)) {
                num++;
            }
            if (!isOperatorF(c)) {
                SymbolNum++;
                SymbolArray[SymbolNum] = input.charAt(j);
            }
            isI = false;
        }
    }
    while (SymbolNum >= 0) {
        RPolish += ',';
        RPolish += SymbolArray[SymbolNum];
        SymbolNum--;
    }
    regex = /,/;
    var RPolishArray = RPolish.split(regex);
    return RPolishArray;
}

function compare(a, b) {
    if ((a.match(/\*/) || a.match(/\//)) && (b.match(/\+/) || b.match(/\-/))) {
        return true;
    } else {
        return false;
    }
}