nested columsn inside bootstrap

1<div class="container-fluid">
2  <div class="col-lg-12">
3      <div class="row">
4        <div class="col-sm-6">
5            <div class="well">
6              <p>First Part</p>
7            </div>
8        </div>
9        <div class="col-sm-6">
10            <div class="well">
11              <p>Second Part</p>
12            </div>
13        </div>
14      </div>
15        <div class="row">
16            <div class="col-sm-6">
17              <div class="well">
18                <div class="row">
19                  <div class="col-md-6">
20                    <div class="well">
21                    <p>Nested 1</p>
22                  </div>
23                  </div>
24                  <div class="col-md-6">
25                    <div class="well">
26                    <p>Nested 2</p>
27                  </div>
28                  </div>
29                </div>
30                <div class="row">
31                  <div class="col-md-6">
32                    <div class="well">
33                    <p>Nested 3</p>
34                  </div>
35                  </div>
36                  <div class="col-md-6">
37                    <div class="well">
38                    <p>Nested 4</p>
39                  </div>
40                  </div>
41                </div>
42            </div>
43
44            </div>
45            <div class="col-sm-6">
46              <div class="well">
47                <p>Fourth Part[enter image description here][1]</p>
48                </div>
49              </div>
50          </div>
51    </div>                      
52</div>
53