algo. reverse paris

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] q = new int[n];
        for (int i = 0; i < n; i++) {
            q[i] = sc.nextInt();
        }
        
        System.out.print(reverse_pairs(q, 0, n - 1));
    }
    
    public static long reverse_pairs(int[] q, int l, int r) {
        if (l >= r) return 0;
        
        int mid = l + r >> 1;
        long num0 = 0, num1 = reverse_pairs(q, l, mid), num2 = reverse_pairs(q, mid + 1, r);
        
        int i = l, j = mid + 1, k = 0;
        int[] tmp = new int[r - l + 1];
        
        while (i <= mid && j <= r) {
            if (q[i] <= q[j]) {
                tmp[k++] = q[i++];
            }
            else {
                tmp[k++] = q[j++];
                num0 += mid - i + 1;
            }
        }
        while (i <= mid) {
            tmp[k++] = q[i++];
        }
        while (j <= r) {
            tmp[k++] = q[j++];
        }
        
        for (int m = l, n = 0; m <= r; m++, n++) {
            q[m] = tmp[n];
        }
        
        return num0 + num1 + num2;
    }
}