#include <iostream>
#include <regex>
#include <string>

int main() {
    std::string text = "My old number was 123-456-7890, but my new number is 987-654-3210.";
    std::regex phone_regex("\\d{3}-\\d{3}-\\d{4}");
    
    std::string result = std::regex_replace(text, phone_regex, "XXX-XXX-XXXX");
    std::cout << result << std::endl;

    return 0;
}