data class P(val a: Int, val b: Long): Comparable<P> {
    override fun compareTo(other: P): Int =
            a.compareTo(other.a)
}

fun main(args: Array<String>) = IO().exec {
    val n = int()
    val m = int()
    val ab = Array(n){P(int(), long())}
    ab.sort()
    val segTree = SegTree(n, 0)
    for (i in n) segTree[i] = ab[i].b
    var ret = 0L
    for (d in 1..m) {
        val k = upperBound(ab, d)
        if (k != 0) {
            val (mb, i) = segTree[0 until k]
            ret += mb
            segTree[i] = -1
        }
    }
    println(ret)
}

fun upperBound(arr: Array<P>, x: Int): Int {
    var ok = arr.size
    var ng = -1
    while (Math.abs(ok - ng) > 1) {
        val mid = (ok + ng) / 2
        if (arr[mid].a > x) {
            ok = mid
        } else {
            ng = mid
        }
    }
    return ok
}

operator fun IntRange.contains(target: IntRange): Boolean = this.first <= target.first && target.last <= this.last
infix fun IntRange.separates(other: IntRange): Boolean = this.last < other.first || other.last < this.first
fun IntRange.size(): Int = this.last + 1 - this.first

class SegTree(val size: Int, val zero: Long) {
    val v = LongArray(size){zero}
    val n = run {
        var n = 1
        while (n < size) n *= 2
        n
    }
    val node = LongArray(2*n-1){zero}
    val inode = IntArray(2*n-1){
        if (it < n-1) 0 else it - (n - 1)
    }
    init {
        for (i in 0 until v.size) node[i+n-1] = v[i]
        for (i in n-2 downTo 0) node[i] = Math.max(node[2*i+1], node[2*i+2])
    }

    operator fun set(x_: Int, value: Long) {
        var x = x_ + n - 1
        node[x] = value
        while (x > 0) {
            x = (x - 1) / 2
            if (node[2*x+1] < node[2*x+2]) {
                node[x] = node[2*x+2]
                inode[x] = inode[2*x+2]
            } else {
                node[x] = node[2*x+1]
                inode[x] = inode[2*x+1]
            }
        }
    }

    operator fun get(query: IntRange): Pair<Long, Int> = getrec(query, 0, 0 until n)

    fun getrec(query: IntRange, k: Int, range: IntRange): Pair<Long, Int> {
        if (query separates range) return Pair(zero, 0)
        if (range in query) return Pair(node[k], inode[k])
        val vl = getrec(query, 2*k+1, with(range){first until (first+last+1)/2})
        val vr = getrec(query, 2*k+2, with(range){(first+last+1)/2 until last+1})
        return if (vl.first < vr.first) vr else vl
    }
}

// region template
operator fun Int.iterator() = 0.until(this).iterator()

class IO {
    val printable = 33..126
    val buffer = ByteArray(1024)
    var ptr = 0
    var buflen = 0
    val out = java.io.PrintWriter(System.out)
    fun hasNextByte(): Boolean = if (ptr < buflen) true else {
        ptr = 0
        buflen = System.`in`.read(buffer)
        buflen > 0
    }

    fun readByte(): Byte = if (hasNextByte()) buffer[ptr++] else -1
    fun hasNext(): Boolean {
        while (hasNextByte() && buffer[ptr] !in printable) ptr++
        return hasNextByte()
    }

    fun string(): String {
        if (!hasNext()) throw java.util.NoSuchElementException()
        val sb = StringBuilder()
        var b = readByte()
        while (b in printable) {
            sb.appendCodePoint(b.toInt())
            b = readByte()
        }
        return sb.toString()
    }

    fun long(): Long {
        if (!hasNext()) throw java.util.NoSuchElementException()
        var n = 0L
        var minus = false
        var b = readByte()
        if (b == '-'.toByte()) {
            minus = true
            b = readByte()
        }
        if (b !in '0'.toByte()..'9'.toByte()) {
            throw NumberFormatException()
        }
        while (true) {
            if (b in '0'.toByte()..'9'.toByte()) {
                n *= 10
                n += b - '0'.toByte()
            } else if (b == (-1).toByte() || b !in printable) {
                return if (minus) -n else n
            } else {
                throw NumberFormatException()
            }
            b = readByte()
        }
    }

    fun int(): Int {
        val nl = long()
        if (nl !in Integer.MIN_VALUE..Integer.MAX_VALUE) throw NumberFormatException()
        return nl.toInt()
    }

    fun double(): Double = string().toDouble()
    fun print(obj: Any) = out.print(obj)
    fun print(i: Int) = out.print(i)
    fun print(l: Long) = out.print(l)
    fun println(obj: Any) = out.println(obj)
    fun println(i: Int) = out.println(i)
    fun println(l: Long) = out.println(l)
    inline fun exec(block: IO.() -> Unit) {
        block()
        out.flush()
    }
}
// endregion

Measured memory_bytes: 76560