Flexbox: how to place two containers side by side?

Question

Flexbox

Good afternoon!
There is the following structure:

With styles:

1 {
  display: flex;
  flex-direction: column;
}

2 {
  flex: 0 0 auto;
}

3 {
  flex: 1 0 auto; /* как расположить слева? */
}

4 {
  flex: 1 0 auto; /* как расположить справа? */
}

5 {
  flex: 0 0 auto;
}

How to arrange containers 3 and 4 in a row WITHOUT wrapping them in an extra container.

Answer 1

https://codepen.io/simkaUser/pen/jwwwMx?editors=0110