Which country has hardest math?

I'm curious to know, which country in the world is renowned for having the most challenging mathematical curriculum? Is there a particular nation that consistently produces students who excel in complex mathematical concepts and problem-solving? Are there any educational systems or cultural factors that contribute to this reputation? I'm eager to learn more about the country that is widely considered to have the hardest math curriculum, and how they achieve such a high level of mathematical proficiency among their students.