The attendee countries’ leaders at the St Petersburg International Economics Forum numbered 68 in 2022, down from 120 in 2021. In 2023 the number rose to 75. I am unable to find the 2024 number. Participation/attendance from business numbered 17,000 in 2023, up from 14,000 in 2022.
https://en.wikipedia.org/wiki/St._Petersburg_International_Economic_Forum
Found it:
“Also, SPIEF 2024 attended by 21,300 participants from 139 countries took part in the events of the St. Petersburg International Economic Forum.”