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

int main( )
{
    std::regex rgx(":((?!.*:).*$)");
    std::smatch match;
    std::string input = "concept:personasia:toby_pizur:personasia:teste";

    if (std::regex_search(input, match, rgx))
    {
        std::cout << match[1];
    }

    return 0;
}