<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<div class="container">
<div class="row">
<div class="col-md-3">
<button id="btn">Open</button>
<input type="date" id="calendar">
</div>
<div class="col-md-3">
<div class="input-group">
<span class="input-group-addon" id="basic-addon1">@</span>
<input type="text" class="form-control" placeholder="Username" aria-describedby="basic-addon1">
</div>
</div>
<div class="col-md-3">
<div class="input-group">
<span class="input-group-addon" id="basic-addon1">@</span>
<input type="text" class="form-control" placeholder="Username" aria-describedby="basic-addon1">
</div>
</div>
<div class="col-md-3">
<div class="input-group">
<span class="input-group-addon" id="basic-addon1">@</span>
<input type="text" class="form-control" placeholder="Username" aria-describedby="basic-addon1">
</div>
</div>
</div>
</div>