How to import RequireJS (AMD) module in Angular 4.x (Angular Cli) App?

I have a legacy JS file, written in the following RequireJS (AMD) module notation:

define('mymodule', [], function(){

    // ... bla bla bla

    return {
        calculate: function() { return 1 + 1; }
    };
});

I'm importing this file from another (legacy) project that uses RequireJS, therefore - I can't change the module definition used.

I want to import it in an Angular Cli (Angular 4.x) app written in TypeScript.

Since Angular Cli uses Webpack 2 to build projects, which supports AMD, I thought I can import it like this:

import * as MyModule from './mymodule.js';

... but that's not working, it triggers an error that the mymodule.js is not a module.

Any ideas (or workarounds) how can I import this legacy module?