function getCoin(){
    let coin = parseInt(localStorage.getItem('MelonCoin'));
    if(isNaN(coin) || coin == null || coin == undefined) coin = 0;
    return coin;
}

function addCoin(amount){
    localStorage.setItem('MelonCoin', getCoin() + amount);
}

function removeCoin(amount){
    localStorage.setItem('MelonCoin', getCoin() - amount);
}