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  hieuminh0157  commented on June 19, 2024, 2:08 a.m.

  include <iostream>

  #include <cmath>
  
  std::string canArrangeMarbles(int n) {
      // Calculate the inverse of the triangular number formula
      double i = (std::sqrt(8 * static_cast<double>(n) + 1) - 1) / 2;
      // Check if i is an integer
      if (i == static_cast<int>(i)) {
          return "Yes.";
      } else {
          return "No.";
      }
  }
  
  int main() {
      int n;
      std::cin >> n;
      std::cout << canArrangeMarbles(n) << std::endl;
      return 0;
  }