1 #include<bits/stdc++.h>
2 using namespace std;
3 const int maxn=1e5+5;
4 typedef long long LL;
5 int n,a[maxn],tmp[maxn];LL ans;
6 void _merge(int l,int m,int r){
7 int i=l,j=m+1,k=l;
8 while(i<=m&&j<=r){
9 if(a[i]>a[j]){tmp[k++]=a[j++];ans+=(LL)m-i+1;}
10 else tmp[k++]=a[i++];
11 }
12 while(i<=m)tmp[k++]=a[i++];
13 while(j<=r)tmp[k++]=a[j++];
14 for(int i=l;i<=r;++i)a[i]=tmp[i];
15 }
16 void _merge_sort(int l,int r){
17 if(l<r){
18 int m=(l+r)>>1;
19 _merge_sort(l,m);
20 _merge_sort(m+1,r);
21 _merge(l,m,r);
22 }
23 }
24 int main(){
25 while(~scanf("%d",&n)){
26 for(int i=0;i<n;++i)scanf("%d",&a[i]);
27 ans=0;_merge_sort(0,n-1);
28 printf("%lld\n",ans);
29 }
30 return 0;
31 }