import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

void main() {
    int x = readint;

    int sum = 0;
    for (int t = 1; ; t++) {
        sum += t;
        if (sum >= x) {
            writeln(t);
            break;
        }
    }
}
