package baekjoon.그리디;
import java.io.BufferedReader;
import java.io.InputStreamReader;
class Main1789 {
public static void main(String[] args) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
long S = Long.parseLong(br.readLine());
long i = 0;
for (; i <= S; i++) {
if (((i * i) + i) / 2 == S) {
System.out.println(i);
break;
}
if (((i * i) + i) / 2 > S) {
System.out.println(i - 1);
break;
}
}
}
}