package codeup_100;
import java.util.Scanner;
public class codeup_87 {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
int sum = 0;
int i = 1;
while(true) {
if(sum>=n) {
System.out.println(sum);break;
}
sum = sum + i;
i++;
}
}
}