Factorial Within Range

Source: Phước Hưng OJ

Version: Phuoc Hung OJ Extended

Problem Statement

Calculate n factorial with a for loop; define 0!=1. The range 0..20 fits signed 64-bit.

Input

One integer n, 0<=n<=20.

Output

n! as a signed 64-bit integer.

Subtasks

• Subtask 1 (20%): 0<=n<=5.
• Subtask 2 (30%): 0<=n<=12.
• Subtask 3 (50%): 0<=n<=20.

Examples

Example 1

Input

0

Output

1

Explanation

The empty product equals 1.

Example 2

Input

5

Output

120

Explanation

Multiply 1 through 5.