fun main() {
    var n = readln().toLong()
    var ans = 0
    while (ans <= n) {
        n -= ans
        ans++
    }
    println(ans - 1)
}

private fun readInt() = readln().toInt()
private fun readLongs() = readStrings().map { it.toLong() }
private fun readStrings() = readln().split(" ")
private fun readInts() = readStrings().map { it.toInt() }