How do I filter images that exceeds an aspect ratio

Question

I'm trying to make a C# program that gets a directory path and iterate on images, then for each image it should check if that Image it's a fit for instagram post and I don't need to crop it.

Some infos about instagram post ratios:

1. Square: 1:1
2. Vertical: 4:5
3. Horizontal 1.91:1.

I'm using these methods to find image aspect ratio

static string FindAspectRatio(int width, int height)
    {
        int gcd = FindGcd(width, height);
        string ratio = $"{width / gcd}:{height / gcd}";
        return ratio;
    }

private static int FindGcd(int x, int y)
    {
        int gcd = 1;
        int temp;

        if (x > y)
        {
            temp = x;
            x = y;
            y = temp;
        }

        for (int i = 1; i < (x + 1); i++)
        {
            if (x % i == 0 && y % i == 0)
                gcd = i;
        }

        return gcd;
    }

then I added 3 if checks for instagram ratios to check with each image. The problem is that sometimes the aspect ratio is not 4:5 but the height is a bit shorter than max aspect ratio instagram allows for vertical posts and on that case I don't need the app to tell me that I should crop that image. Is there anyway to achieve this so the app can exactly tell when an image should be cropped?

if (aspectRatio == "4:5" || aspectRatio == "1:1" || aspectRatio == "16:9")
{
    continue;
}

Answer 1

Okay I was able to solve it by experimenting with different values,

static bool InstaRatioValid(decimal ratio)
{
    if(ratio >= 0.80M && ratio <= 1.92M)
    {
        return true;
    }
    return false;
}

static decimal FindAspectRatio(int width, int height)
{
    decimal ratio = Math.Round((decimal)width / height, 2,MidpointRounding.ToZero);
    return ratio;
}