function a2hex(str) {
        var arr = [];
        for (var i = 0, l = str.length; i < l; i ++) {
            var hex = Number(str.charCodeAt(i)).toString(16).padStart(2,'0');
            arr.push(hex);
        }
        return arr.join('');
    }

    function toAddr(str){
        return "0x" + a2hex(str);
    }

    var Web3 = require('web3');
    var web3 = new Web3();
    web3.setProvider(new Web3.providers.HttpProvider('https://ropsten.infura.io/')); // https://ropsten.etherscan.io/
    var criticoContractABI =[{"constant": true,"inputs": [{"name": "flag","type": "address"}],"name": "doSomething","outputs": [{"name": "","type": "bool"}],"payable": false,"stateMutability": "pure","type": "function"}];

    var critico = web3.eth.contract(criticoContractABI);
    var critInstance = critico.at('0x44f0d8e171c79da5318f4e72a848be7f0ea1cad3'); // contract address
    $('.submit-button').click(function() {
        $(".message").text("Checking...");
        var ret = critInstance.doSomething.call(toAddr($(".text-input").val()));
        if (ret)
            $(".message").text("Congratz, submit it with flag format!");
        else
            $(".message").text("Nah!");
    });