import java.util.*;

class Solution {
  public int number_of_disc_intersections ( int[] A ) {
    int overlaps = 0;
    if (A.length<2) return 0;
    PriorityQueue<Integer> leftEdges = new PriorityQueue<Integer>();
    PriorityQueue<Long> rightEdges = new PriorityQueue<Long>();
    for (int i=0; i<A.length; i++){
      leftEdges.add(i-A[i]);
      rightEdges.add((long)i+(long)(A[i]));
    }
    int otherCirclesAtThisEdgeNum = 0;
    while ( !rightEdges.isEmpty()) {
      try {
        if (leftEdges.element() <= rightEdges.peek() ) {
          overlaps += otherCirclesAtThisEdgeNum++;
          if (overlaps > 10000000) return -1;
          leftEdges.poll();
        } else {
          otherCirclesAtThisEdgeNum--;
          rightEdges.poll();
        }
      }catch (NoSuchElementException e){
        break;
      }
    }
    return overlaps;
  }
}