题目链接:点击打开链接
import java.math.*;
import java.util.*;
import java.io.*;
public class Solution {
public void work() {
int n;
while (cin.hasNext()) {
n = cin.nextInt();
BigInteger tmp = BigInteger.ONE;
for(int i = 3; i < n; i ++) {
tmp = tmp.multiply(BigInteger.valueOf(i));
}
BigInteger ans = tmp;
for(int i = n-1; i >= 3; i --) {
tmp = tmp.multiply(BigInteger.valueOf(n)).divide(BigInteger.valueOf(n-i));
ans = ans.add(tmp);
}
System.out.println(ans);
}
}
Solution() {
cin = new Scanner(System.in);
}
public static void main(String[] args) {
Solution e = new Solution();
e.work();
}
public Scanner cin;
}