fun main() {
    val n_num = readLine()!!.toInt();
    val arr = Array(n_num) {
        readLine()!!.toInt()
    }
    arr.sort()
    
    var now = -3
    var cnt = 1
    for (i in arr.indices) {
        val ai = arr[i]
        if (now + 1 < ai) {
            now = ai
        } else {
            now = ai
            cnt++
        }
    }

    println(cnt)
}