codenul.js

/*******
 * Read input from STDIN
 * Use: console.log()  to output your result.
 * Use: console.error() to output debug information into STDERR
 * ***/

var input = [];

readline_object.on("line", (value) => { //Read input values
	input.push(value);
})
//Call ContestResponse when all inputs are read
readline_object.on("close", ContestResponse); 

function getId() {
    return Math.random().toString(16).substr(2, 8);
}

function ContestResponse(){
    
    // first step: get a ordered list of all the points
    let points = []
    input.slice(1).forEach(e => {
        let r = e.split(' ')
        let id = getId()
        let start = parseInt(r[0])
        let end = parseInt(r[1])
        points.push({id, pos: start, as: 'start'})
        points.push({id, pos: end, as: 'end'})
    })
    points.sort((a, b) => a.pos - b.pos)
    
    let activeZones = [] // list of active zone id
    let zonesCount = 0
    // cursor
    points.forEach((p, i) => {
        console.error(p.pos)
        if (p.as == 'start') {
            activeZones.push(p.id)
        }
        if (p.as == 'end') {
            activeZones = activeZones.filter(d => d != p.id)
        }
        if (activeZones.length == 0 && points[i+1] != undefined && points[i+1].pos != p.pos+1 && points[i+1].pos != p.pos) {
            zonesCount = zonesCount + 1
        }
    })
    
    
    console.error(points)
    
    console.log(zonesCount+1)
    
    
    
    
    
}