求调

#include<bits/stdc++.h>
using namespace std;
int n,a[1000000],b[100000],ans;
void s(int l,int r){
	if(r<=l) return;
	int m=(l+r)/2;
	s(l,m);s(m+1,r);
	int h1=l,h2=m+1,h=l;
	while(h1<=m&&h2<=r){
		if(a[h1]<a[h2])
			b[h++]=a[h1++];
		else b[h++]=a[h2++],ans+=m-h1+1; 
	}
	while(h1<m) b[h++]=a[h1++];
	while(h2<=r) b[h++]=a[h2++];
	for(int i=l;i<=r;i++) a[i]=b[i];
}//归并排序 
int main(){a
	ios::sync_with_stdio(false);
	cin>>n;
	for(int i=1;i<=n;i++) cin>>a[i];
	s(1,n);
	cout<<ans;
	return 0;
}