var currentNum = 0;

function showHideContent(num) {
    document.getElementById('link' + num).className = 'selected';
    if (currentNum != 0) {
        document.getElementById('link' + currentNum).className = '';
    }
    document.getElementById('content' + num).className = 'content-div';
    document.getElementById('content' + currentNum).className = 'content-div content-div-hidden';
    
    currentNum = num;
}