What will the program with multiple catch blocks output

It is necessary to predict which set of characters will appear in the standard output after executing the following program.

#include <iostream>

using namespace std;

struct boom_exception : public std::exception {};
struct primary_exception : public std::exception {};

struct Explosive
{
    ~Explosive()
    {
        // destructor does nothing
    }
};

int main()
{
    try
    {
        Explosive explosiveObj;
        throw primary_exception();
    }
    catch (const std::exception&)
    {
        cout << "1";
        // handler 1
    }
    catch (primary_exception&)
    {
        cout << "2";
        // handler 2
    }
    catch (boom_exception&)
    {
        cout << "3";
        // handler 3
    }
    catch (int&)
    {
        cout << "4";
        // handler 4
    }

    return 0;
}