package main

import (
	"fmt"
)

func main() {
	var n int64
	if _, err := fmt.Scan(&n); err != nil {
		return
	}
	count := 0
	for h := int64(1); h*(3*h+1)/2 <= n; h++ {
		if (n+h)%3 == 0 {
			count++
		}
	}
	fmt.Println(count)
}