/Dãy nghịch thế

              #include <iostream>
        using namespace std;
        
        #define SIZE 60001
        int n;
        int res = 0;
        int maxArr = 0;
        int arr[SIZE];
        int tree[SIZE * 4];
        
        int getSum(int index, int left, int right, int a, int b) {
          if (left > b || right < a) return 0;
          if (left >= a && right <= b) return tree[index];
        
          int mid = (left + right) / 2;
        
          return getSum(index * 2, left, mid, a, b) + getSum(index * 2 + 1, mid + 1, right, a, b);
        }
        
        void update(int index, int left, int right, int a, int b, int val) {
          if (left > b || right < a) return;
          if (left == right) {
            tree[index] += val;
            return;
          }
        
          int mid = (left + right) / 2;
        
          update(index * 2, left, mid, a, b, val);
          update(index * 2 + 1, mid + 1, right, a, b, val);
        
          tree[index] = tree[index * 2] + tree[index * 2 + 1];
        }
        
        int main() {
          cin >> n;
        
          for (int i = 1; i <= n; i++) {
            cin >> arr[i];
            maxArr = max(maxArr, arr[i]);
          }
        
          for (int i = n; i >= 1; i--) {
            int t = getSum(1, 1, maxArr, 1, arr[i] - 1);
            res = res + t;
            //cout << i << " - ";
            update(1, 1, maxArr, arr[i], arr[i], 1);
          }
        
          cout << res << endl;
        
          return 0;
        }