static int binarySearch(int[] cost, int element, int left, int right){
        if(left == right){
            if(cost[left] != element) return -1;
            else return left;
        }

        int middle = (left+right)/2;
        if(cost[middle] == element) return middle;
        else if(cost[middle]<element)
            return binarySearch(cost, element, middle+1, right);
        else return binarySearch(cost, element, left, middle-1);

    }