1 #include <iostream>
 2 using namespace std;
 3 
 4 const int N=1000005;
 5 int num[N];
 6 int temp[N];
 7 long long ans;
 8 
 9 void merge(int left,int mid,int right)
10 {
11     int i=left,j=mid+1;
12     int p=0;
13     while (i<=mid&&j<=right)
14     {
15         if (num[i]<=num[j])  temp[p++]=num[i++];
16         else
17         {
18             ans+=mid-i+1;       //就是num[j]到num[i]要经过几次调换
19             temp[p++]=num[j++];
20         }
21     }
22     while (i<=mid)  temp[p++]=num[i++];
23     while (j<=right)     temp[p++]=num[j++]; 
24     j=left;
25     for (i=0;i<p;i++)
26         num[j++]=temp[i];
27 }
28 
29 void mergesort(int left,int right)
30 {
31     int mid;
32     if (left<right)
33     {
34         mid=(left+right)/2;
35         mergesort(left,mid);    //左边还可以分的话，归并左边
36         mergesort(mid+1,right); //右边可以分的话，归并右边
37         merge(left,mid,right);  //合并两个已经并好的
38     }
39 }
40 
41 int main()
42 {
43     int n,i;
44     while (scanf("%d",&n)!=EOF)
45     {
46         ans=0;
47         for (i=0;i<n;i++) 
48             scanf("%d",&num[i]);
49         mergesort(0,n-1);
50         printf("%lld\n",ans);
51     }
52     return 0;
53 }