o15_oct_inversion

#include <bits/stdc++.h>

using namespace std;
using lli = long long;
const int N = 1e5;
int fw[N + 10], ar[N + 10];
vector <int> num;
int n, sz;

void Update(int pst){
    for(int i=pst;i<=sz;i+=i&-i)
        fw[i] ++;
}

int Sum(int pst, int sum = 0){
    for(int i=pst;i>=1;i-=i&-i)
        sum += fw[i];
    return sum;
}

int main(){

    scanf("%d", &n);

    for(int i=1;i<=n;i++){
        scanf("%d", &ar[i]);
        num.push_back(ar[i]);
    }

    sort(num.begin(), num.end());
    num.resize( unique(num.begin(), num.end()) - num.begin() );
    sz = num.size();

    lli ans = 0;
    for(int i=1;i<=n;i++){
        int idx;
        {
            int l = 0, r = sz - 1;
            while(l <= r){
                int mid = (l + r) / 2;
                if(num[mid] == ar[i]){
                    idx = mid + 1;
                    break;
                }
                else if(num[mid] < ar[i]) l = mid + 1;
                else r = mid - 1;
            }
        }
        ans += Sum(sz) - Sum(idx);
        Update(idx);
    }

    printf("%lld", ans);

    return 0;
}