#include<bits/stdc++.h>
using namespace std;
const int N=5e6+2840;
long long n,ans,a[N],b[N];
void m(int l,int r){
	if(l==r)return;
	int mid=l+r>>1;
	m(l,mid);
	m(mid+1,r);
	int i=l,j=mid+1,k=l;
	while(i<=mid&&j<=r){
		if(a[i]<=a[j]){
			b[k++]=a[i++];
		}else{
			b[k++]=a[j++];
			ans+=mid-i+1; 
		}
	} 
	while(i<=mid){
		b[k++]=a[i++];
	}
	while(j<=r)
		b[k++]=a[j++];
		for(int i=l;i<=r;i++)
		a[i]=b[i];
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	m(1,n);
	cout<<ans;
	return 0;
}
//带飞

归并排序

#include<bits/stdc++.h>
using namespace std;
const int N=5e5+5,INF=0x3f3f3f3f;
typedef long long LL;
LL n,a[N],b[N],ans;
void mergesort(int l,int r){
	if(l==r)return;
	int mid=l+r>>1;
	mergesort(l,mid);
	mergesort(mid+1,r);
	int i=l,j=mid+1,k=l;
	while(i<=mid&&j<=r){
		if(a[i]<=a[j])b[k++] = a[i++];
		else b[k++] = a[j++],ans+=mid-i+1;
	}
	while(i<=mid)b[k++] = a[i++];
	while(j<=r)b[k++] = a[j++];
	for(int i=l;i<=r;i++)a[i] = b[i];
}
int main()
{
	cin>>n;
	for(int i=1;i<=n;i++)cin>>a[i];
	mergesort(1,n);
	cout<<ans;
	return 0;
}

#include <iostream>
#include <vector>
#define int long long 
using namespace std;
int ans=0;
void mergesort(vector<int>&a,int l,int mid,int r){
	int *tmp=new int[r-l+1];
	int i=l,j=mid+1,index=0;
	while(i<=mid&&j<=r){
		if(a[i]<=a[j])tmp[index++]=a[i++];
		else{
			tmp[index++]=a[j++];
			ans+=mid-i+1;
		}
	}
	while(i<=mid)tmp[index++]=a[i++];
	while(j<=r)tmp[index++]=a[j++];
	for(int i=0;i<index;i++){
		a[l+i]=tmp[i];
	}
	delete[]tmp;
}
void merge_up2down(vector<int>&a,int l,int r){
	if(l>=r)return;
	int mid=(l+r)>>1;
	merge_up2down(a,l,mid);
	merge_up2down(a,mid+1,r);
	mergesort(a,l,mid,r);
}
signed main(){
	int n;
	cin>>n;
	vector<int> a(n);
	for(int i=0;i<n;i++)cin>>a[i];
	merge_up2down(a,0,n-1);
	cout<<ans<<endl;
	return 0;
}