动态开点 + 权值线段树做法，全WA求调！！

RT

#include <bits/stdc++.h>
#define int long long
#define H 19260817
#define rint register int
#define For(i,l,r) for(rint i=l;i<=r;++i)
#define FOR(i,r,l) for(rint i=r;i>=l;--i)
#define MOD 1000003
#define mod 1000000007

using namespace std;

inline int read() {
  rint x=0,f=1;char ch=getchar();
  while(ch<'0'||ch>'9'){if (ch=='-') f=-1;ch=getchar();}
  while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
  return x*f;
}

void print(int x){
  if(x<0){putchar('-');x=-x;}
  if(x>9){print(x/10);putchar(x%10+'0');}
  else putchar(x+'0');
  return;
}

const int N = 500010 * log(1e9);

struct Node {
    int ls, rs;
    int l, r;
    int num; 
}t[N << 2];

int n = read(), a[N], ans, mx, idx = 1;

void pushup(int p) {
    t[p].num = t[t[p].ls].num + t[t[p].rs].num;
}

void add(int p, int l, int r, int k) {
    t[p].l = l, t[p].r = r;
    if(l == r) {
        t[p].num ++;
        return ;
    }
    int mid = l + r >> 1;
    if(k <= mid) {
        if(!t[p].ls) t[p].ls = ++idx;
        add(t[p].ls, l, mid, k);
    } else {
        if(!t[p].rs) t[p].rs = ++idx;
        add(t[p].rs, mid + 1, r, k);
    }
    pushup(p);
}

int query(int p, int l, int r) {
    if(p == 0) return 0;
    if(l <= t[p].l && t[p].r <= r) {
        return t[p].num;
    }
    int mid = t[p].l + t[p].r >> 1, ans = 0;
    if(l <= mid) {
        ans += query(t[p].ls, l, r);
    } 
    if(r > mid) {
        ans += query(t[p].rs, l, r);
    }
    return ans;
}

signed main() {
    For(i,1,n) a[i] = read(), mx = max(mx, a[i]);
    For(i,1,n) {
        add(1, 1, n, a[i]);
        ans += query(1, a[i] + 1, mx);
    }
    cout << ans << '\n';
    return 0;
}