put words in a input

<html>
<body>
    <input type="text" placeholder="Busca algo" id="in" onclick="buscar()">
    <button id="boton" onclick="search()">Search</button>

    <script>
    function buscar() {
    var input = document.getElementById("in");
    input.innerHTML = "mary poppins";
    }
    </script>
</body>
</html>