#include<iostream>
#include<cstring>
#define N 500005
#define ll long long
using namespace std;
ll n, ans, a[N], c[N], r[N];
ll read(){
	ll x = 0, f = 1;
	char c = getchar();
	while(c < '0' || c > '9'){
		if(c == '-') f = -1;
		c = getchar();
	}
	while(c >= '0' && c <= '9'){
		x = x * 10 + c - '0';
		c = getchar();
	}
	return x * f;
}
ll lowbit(ll x){
	return x & -x;
}
void add(ll x, ll y){
	for(ll i = x; i <= n; i += lowbit(i)){
		c[i] += y;
	}
}
ll getsum(ll x){
	ll sum = 0;
	for(ll i = x; i > 0; i -= lowbit(i)){
		sum += c[i];
	}
	return sum;
}
int main(){
	n = read();
	for(ll i = 1; i <= n; i++){
		a[i] = read();
	}
	for(ll i = n; i >= 1; i--){
		r[i] = getsum(a[i] - 1);
		add(a[i], 1);
		ans += r[i];
	}
	printf("%lld", ans);
	return 0;
} 

我数组已经开够了，但还是全RE，求助QwQ