How to make clearRect round in JavaScript?

Question

JavaScript

Hello, I have such canvas and such js
<canvas id="c1" width="450" height="450"></canvas>

var canvas = document.getElementById('c1');
var ctx = canvas.getContext('2d');


ctx.fillStyle = '#00bf54';
ctx.fillRect(0, 0, 450, 450);
    canvas.onmousedown = function (event) {
        canvas.onmousemove = function (event) {
        var x = event.clientX;
        var y = event.clientY;
        ctx.clearRect(x+0, y+0, 45, 45);

    }
    canvas.onmouseup = function () {
        canvas.onmousemove = null;
    }
}

when clicked and moved, the canvas block is removed through clearRect with squares.
How to make circles instead of squares?