1 // 687950    zhuli19901106    1348    Accepted    点击此处查看所有case的执行结果    1800KB    1093B    100MS
 2 // 201401302316
 3 #include <cstdio>
 4 using namespace std;
 5 
 6 const int MAXN = 100005;
 7 int a[MAXN];
 8 int n;
 9 long long int res;
10 int tmp[MAXN];
11 
12 void merge_sort_recursive(int a[], int ll, int rr)
13 {
14     if (ll >= rr) {
15         return;
16     }
17     int mm;
18     mm = (ll + rr) / 2;
19     merge_sort_recursive(a, ll, mm);
20     merge_sort_recursive(a, mm + 1, rr);
21 
22     int i, j, k;
23 
24     i = ll;
25     j = mm + 1;
26     k = ll;
27     while (true) {
28         if (i <= mm) {
29             if (j <= rr) {
30                 if (a[i] <= a[j]) {
31                     tmp[k++] = a[i++];
32                 } else {
33                     tmp[k++] = a[j++];
34                     res += mm - i + 1;
35                 }
36             } else {
37                 tmp[k++] = a[i++];
38             }
39         } else {
40             if (j <= rr) {
41                 tmp[k++] = a[j++];
42             } else {
43                 break;
44             }
45         }
46     }
47     for (i = ll; i <= rr; ++i) {
48         a[i] = tmp[i];
49     }
50 }
51 
52 int main() 
53 {
54     int i;
55 
56     while (scanf("%d", &n) == 1) {
57         for (i = 0; i < n; ++i) {
58             scanf("%d", &a[i]);
59         }
60         res = 0;
61         merge_sort_recursive(a, 0, n - 1);
62         printf("%lld\n", res);
63     }
64 
65     return 0;
66 }