JAVA 代码

import java.util.Scanner;

public class  Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        work(n);
    }

    static void work(int n) {
        long[][] f = new long[2001][2001];
        f[1][1] = 1;
        if (n == 1) {
            System.out.println(1);
            return;
        }
        for (int i = 2; i <= 2000; i++) {
            for (int j = 1; j <= i; j++) {
                f[i][j] = f[i - 1][j] + f[i - 1][j - 1];
                if (f[i][j] == n) {
                    System.out.println(1l * i * (i - 1) / 2 + j);
                    return;
                }
            }
        }
        long sqrt = (long) Math.sqrt(n * 2);
        if (sqrt * (sqrt + 1) == 2 * n) {
            System.out.println(1l * (sqrt+2) * (1 + sqrt) / 2 + 3);
            return;
        }
        System.out.println(1l * n * (n + 1) / 2 + 2);
    }
}