UICollectionView Horizontal Paging by 2 items

Question

Hello I need a collection view layout as in the following picture. I create a UICollectionViewFlowLayout subclass and wrote these codes but whenever I scroll the items, they paging by scrolling speed not 2-2, But I want to scroll by 2-2 pages of indexes in every scroll.

Thanks

Here are my codes:

  - (void)awakeFromNib
   {
    self.minimumInteritemSpacing = 5.0;
    self.minimumLineSpacing = 5.0;
    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    self.sectionInset = UIEdgeInsetsMake(0.0, 5.0, 0.0, 5.0);
    self.collectionView.decelerationRate = UIScrollViewDecelerationRateFast;
    self.itemSize = CGSizeMake((self.collectionView.frame.size.width - self.minimumLineSpacing * 2 - self.sectionInset.left)/2,self.collectionView.frame.size.height);
}

-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{

    CGFloat offsetAdjustment = MAXFLOAT;
    CGFloat horizontalOffset = proposedContentOffset.x;

    CGRect targetRect = CGRectMake(proposedContentOffset.x, 0, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);

    NSMutableArray *array = [super layoutAttributesForElementsInRect:targetRect];

    for (UICollectionViewLayoutAttributes *layoutAttributes in array) {

        CGFloat itemOffset = layoutAttributes.frame.origin.x;

        if (ABS(itemOffset - horizontalOffset) < ABS(offsetAdjustment)) {

            offsetAdjustment = itemOffset- horizontalOffset - self.sectionInset.left;

        }
    }
    proposedContentOffset.x += offsetAdjustment;

    return CGPointMake(proposedContentOffset.x, proposedContentOffset.y);
}