function solution(lines) {
    var answer = 0;
    
    
    const getStartEndMilliSeconds = (str) => {
        const [yms, endTime, duration] = str.split(' ')
        const date = new Date(`${yms} ${endTime}`)
        const endMilliSeconds = date.getTime();
        const startMilliSeconds = endMilliSeconds - duration.slice(0, -1)* 1000 + 1;
        
        return [startMilliSeconds , endMilliSeconds ]
    
    }
    
    const timeStamp = []
    
    lines.map(line => {
        const [start, end] = getStartEndMilliSeconds(line)
        timeStamp.push([start - 1000, 'start'])
        timeStamp.push([end])
    })
    
    let count =0;
    let max =-Infinity;
    
    timeStamp.sort((a,b) => a[0] - b[0]).forEach(([time, isStart]) => {
        count += isStart ? 1 : -1;
        
        max = Math.max(count, max);
    })
    
    return max;
}