fun main(){
    var (n, k) = readLine()!!.split(" ").map{it.toInt()}
    val x = readLine()!!.split(" ").map{it.toInt()}
    val a = readLine()!!.split(" ").map{it.toInt()}
    
    k--
    var lindex = k
    var rindex = k
    var lpos = x[lindex]-a[lindex]
    var rpos = x[rindex]+a[rindex]

    while(true){
        if(lindex > 0 && lpos <= x[lindex-1]){
            lindex--
            lpos = Math.min(lpos, x[lindex]-a[lindex])
            rpos = Math.max(rpos, x[lindex]+a[lindex])
        }else if(rindex+1 < n && x[rindex+1] <= rpos){
            rindex++
            lpos = Math.min(lpos, x[rindex]-a[rindex])
            rpos = Math.max(rpos, x[rindex]+a[rindex])
        }else{
            break
        }
    }

    println(rpos-lpos+1)
}