Analyze the image and extract all mathematical formulas and diagrams.

Mathematical Content:

• A circle diagram with labels R (radius) and D (diameter). The center of the circle is marked. A radius line is drawn, and the diameter line is also visible.
• The formula for the area of a circle: S = πR²
• The number '26.' is present in the upper left corner, likely a date or item number.
• Some illegible handwritten text in what appears to be Cyrillic script is present on the right side of the board.