Divs don't float how I would - html

Question

I've 5 divs in a single div, that I would make it floats 2 at left and 3 at right:
.container {
height: 400px;
border: 1px solid black;
}
.first, .second, .third, .fourth, .fifth {
width: 50%;
}
.first {
height: 300px;
background-color: red;
float: left;
}
.second {
height: 100px;
background-color: blue;
float: left;
}
.third {
height: 100px;
background-color: green;
float: right;
}
.fourth {
height: 200px;
background-color: yellow;
float: right;
}
.fifth {
height: 100px;
background-color: aquamarine;
float: right;
}
<div class="container">
<div class="first"> FIRST </div>
<div class="second"> SECOND </div>
<div class="third"> THIRD </div>
<div class="fourth"> FOURTH</div>
<div class="fifth"> FIFTH </div>
</div>
I would like that they were placed:
FIRST and SECOND at left
THIRD, FORTH and FIFTH at right.
Instead, they are placed like:
FIRST and FIFTH at left
SECOND, THIRD and FOURTH at right.
Do you know how fix it? Here there is my code: https://jsfiddle.net/82bkdbpn/

Answer 1

Since you have defined fixed height on container element you can use Flexbox to do this and define flex-direction: column.
.container {
height: 400px;
border: 1px solid black;
display: flex;
flex-direction: column;
flex-wrap: wrap;
}
.first, .second, .third, .fourth, .fifth {
width: 50%;
height: 100px;
}
.first {
height: 300px;
background-color: red;
}
.fourth {
height: 200px;
background-color: yellow;
}
.second {background-color: blue;}
.third {background-color: green;}
.fifth {background-color: aquamarine;}
<div class="container">
<div class="first"> FIRST </div>
<div class="second"> SECOND </div>
<div class="third"> THIRD </div>
<div class="fourth"> FOURTH</div>
<div class="fifth"> FIFTH </div>
</div>

Answer 2

You can wrap the divs in Columns, and float these two. Or you can use flexbox, there is a very good answer from Nenad Vracar about this.
Here is an example with two column wrapper div elements:
.container {
height: 400px;
border: 1px solid black;
}
.col {
width: 50%;
float: left;
}
.first {
height: 300px;
background-color: red;
}
.second {
height: 100px;
background-color: blue;
}
.third {
height: 100px;
background-color: green;
}
.fourth {
height: 200px;
background-color: yellow;
}
.fifth {
height: 100px;
background-color: aquamarine;
}
<div class="container">
<div class="col">
<div class="first"> FIRST </div>
<div class="second"> SECOND </div>
</div>
<div class="col">
<div class="third"> THIRD </div>
<div class="fourth"> FOURTH</div>
<div class="fifth"> FIFTH </div>
</div>
</div>