SEQPAIR

#include <stdio.h>
#define maxn 1000000

int a[maxn];
int temp[maxn];
int n;
int cnt = 0;

void merge (int l, int k, int r) {
    int i = l, j = k+1, v = 0;
    while (i <= k && j <= r) {
        if (a[i] < a[j]) {
            temp[v] = a[j];
            cnt += (k-i+1);
            ++j;
        } else {
            temp[v] = a[i];
            ++i;
        }
        ++v;
    }
    while (i <= k) {
        temp[v] = a[i];
        ++i;
        ++v;
    }
    while (j <= r) {
        temp[v] = a[j];
        ++j;
        ++v;
    }

    for (i = l; i <= r; ++i) {
        a[i] = temp[i-l];
    }
    return;
}

void MergeSort (int l, int r) {
    if (l < r) {
        int k = (l+r)/2;
        MergeSort(l, k);
        MergeSort(k+1, r);
        merge(l, k, r);
    }
}

int main () {
    scanf("%d", &n);
    for (int i = 1; i <= n; ++i) {
        scanf("%d", &a[i]);
    }
    MergeSort(1, n);
    printf("%d\n", cnt);
    return 0;
}