Codeforces Parking Lot

http://codeforces.com/problemset/problem/630/I

简单的排列组合，推式子技巧：举一个小样例，看着推，别抽象着推，容易错

#include <iostream>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#include <cstring>
#define inf 2147483647
#define N 1000010
#define p(a) putchar(a)
#define For(i,a,b) for(long long i=a;i<=b;++i)using namespace std;
long long n;
void in(long long &x){
    long long y=;char c=getchar();x=;
    while(c<''||c>''){if(c=='-')y=-;c=getchar();}
    while(c<=''&&c>=''){ x=(x<<)+(x<<)+c-'';c=getchar();}
    x*=y;
}
void o(long long x){
    if(x<){p('-');x=-x;}
    if(x>)o(x/);
    p(x%+'');
}long long ksm(long long a,long long b){
    long long r=;
    while(b>){
        if(b&)
            r=r*a;
        a=a*a;
        b>>=;
    }
    return r;
}int main(){
    in(n);
    o((*n-)*ksm(,n-));
    return ;
}