function processData(input) {
    let frontStack = new Array();
    let tailStack = new Array();
    let regex = /(?<=\n)(?<type>\d)\s*?(?<value>\d*)(?=(\n|$))/g;
    let inputObjArr = [...input.matchAll(regex)].map((result) => (
        {
            'type': Number(result.groups.type),
            'value': result.groups.value
        }
    ));
    inputObjArr.forEach((inputObj) => {
        switch(inputObj.type){
            case 1: {
                tailStack.push(inputObj.value);
                break;   
            }
            case 2: {
                if(frontStack.length === 0){
                    while(tailStack.length > 0){
                        frontStack.push(tailStack.pop());
                    }
                }
                frontStack.pop();
                break;
            }
            case 3: {
                if(frontStack.length === 0){
                    while(tailStack.length > 0){
                        frontStack.push(tailStack.pop());
                    }
                }
                console.log(frontStack.at(-1))
                break;
            }
        }
    })
}