let result = "";
const history = [""];

function processCommand(input) {
    const [command, option] = input.split(" ");
    switch (command) {
        case "1":
            result += option;
            history.push(result);
            break;
        case "2":
            result = result.slice(0, result.length - option);
            history.push(result);
            break;
        case "3":
            console.log(result[option - 1]);
            break;
        case "4":
            history.pop();
            result = history.at(-1);
            break;
        default:
            break;
    }
}

function processData(input) {
    input.split(/\r?\n/).slice(1).forEach(processCommand);
}