<p>Write a program to count the number of days between two dates.</p> <p>The two dates are given as strings, their format is <code>YYYY-MM-DD</code> as shown in the examples.</p> <p> </p> <p><strong class="example">Example 1:</strong></p> <pre><strong>Input:</strong> date1 = "2019-06-29", date2 = "2019-06-30" <strong>Output:</strong> 1 </pre><p><strong class="example">Example 2:</strong></p> <pre><strong>Input:</strong> date1 = "2020-01-15", date2 = "2019-12-31" <strong>Output:</strong> 15 </pre> <p> </p> <p><strong>Constraints:</strong></p> <ul> <li>The given dates are valid dates between the years <code>1971</code> and <code>2100</code>.</li> </ul>