import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    private static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    private static int n;

    // 组合数
    private static long C(int a, int b) {
        long res = 1;
        for (int i = a, j = 1; j <= b; i --, j ++) {
            res = res * i / j;
            if (res > n) return res;
        }
        return res;
    }

    private static boolean check(int k) {
        long l = k * 2, r = n;
        while (l < r) {
            long mid = l + r >> 1;
            if (C((int) mid, k) >= n) r = mid;
            else l = mid + 1;
        }

        if (C((int) r, k) != n) return false;

        System.out.println(r * (r + 1) / 2 + k + 1);

        return true;
    }

    public static void main(String[] args) throws IOException {
        n = Integer.parseInt(reader.readLine());

        for (int k = 16; ; k --)
            if (check(k)) break;

        reader.close();
    }
}