include[HTML_REMOVED]
using namespace std;
typedef long long LL;
const int N=1e5+10;
int a[N],tem[N];
LL merge_sort(int q[],int l,int r)
{
if(l>=r)return 0;
int mid=l+r>>1;//注意这里不是q[r+l>>1]
LL res=merge_sort(q,l,mid)+merge_sort(q,mid+1,r);
int k=0,i=l,j=mid+1;
while(i<=mid&&j<=r)
if(q[i]<=q[j])tem[k++]=q[i++];
else {
res+=mid-i+1;
tem[k++]=q[j++];
}
while(i<=mid)tem[k]=q[i];
while(j<=r)tem[k]=q[j];
for(i=l,j=0;i<=r;i,j)q[i]=tem[j];
return res;
}
int main()
{
int n;
scanf(“%d”,&n);
for(int i=0;i<n;i++)scanf(“%d”,&a[i]);
cout<<merge_sort(a,0,n-1)<<endl;
return 0;
}