#include <bits/stdc++.h>

#define int long long

using namespace std;

int read() {
    int x = 0, k = 1;
    char c = getchar();
    while (c < '0' || c > '9') {
        if (c == '-') k = -1;
        c = getchar();
    }
    while (c >= '0' && c <= '9') {
        x = x * 10 + c - '0';
        c = getchar();
    }
    return x * k;
}

#define N 500005

struct node {
	int x, id;
	friend bool operator < (const node a, const node b) {
		return a.x < b.x;
	}
} t[N];

struct segt {
	int l, r, dat;
} a[N << 2];

namespace segment_tree {
	
	void build(int p, int l, int r) {
		a[p].l = l; a[p].r = r;
		if (l == r) return ;
		int mid = l + r >> 1;
		build(p << 1, l, mid);
		build(p << 1 | 1, mid + 1, r);
	}
	
	int query(int p, int l, int r) {
		if (a[p].l >= l && a[p].r <= r) return a[p].dat;
		int mid = a[p].l + a[p].r >> 1, sum = 0;
		if (l <= mid) sum += query(p << 1, l, r);
		if (r > mid) sum += query(p << 1 | 1, l, r);
		return sum;
	}
	
	void update(int p, int w, int x) {
		if (a[p].l == w && a[p].r == w) {
			a[p].dat += x; return ;
		}
		int mid = a[p].l + a[p].r >> 1;
		if (w <= mid) update(p << 1, w, x);
		else update(p << 1 | 1, w, x);
		a[p].dat = a[p << 1].dat + a[p << 1 | 1].dat; 
	}
	
}

using namespace segment_tree;

int n, d[N];
long long ans;

signed main() {
//	freopen("input.txt", "r", stdin);
//	freopen("output.txt", "w", stdout);
	n = read();
	for (int i = 1; i <= n; i++)
		t[i] = {read(), i};
	sort(t + 1, t + n + 1);
	for (int i = 1; i <= n; i++)
		d[t[i].id] = i;
		
	build(1, 1, n);
	for (int i = 1; i <= n; i++) {
		ans += query(1, d[i] + 1, n);
		update(1, d[i], 1);
	}
	printf("%lld", ans);
}

rt，第 6 个点就错，发现输出比答案大了 2。