# Constants

This Go code demonstrates the use of constants, basic arithmetic operations, and a function from the `math` package. Let's go through each part of the code:

```go
package main

import (
	"fmt"
	"math"
)

// Declare a constant 's' with type string and initialize it with the value "constant"
const s string = "constant"

func main() {
	// Print the value of the constant 's'
	fmt.Println(s)

	// Declare a constant 'n' and initialize it with the value 500000000
	const n = 500000000

	// Declare a constant 'd' and initialize it with the result of the expression 3e20 / n
	const d = 3e20 / n
	fmt.Println(d)

	// Print the value of 'd' after converting it to int64
	fmt.Println(int64(d))

	// Print the result of the sine function applied to 'n' from the math package
	fmt.Println(math.Sin(n))
}
```

When you run this Go program, it will output the values of the constants and the result of the mathematical operations to the console.

The output should be something like:

```
constant
6e+11
600000000000
-0.28470407323754404
```

### Explanation:

1. `const s string = "constant"`: Declares a constant named `s` of type string and initializes it with the value "constant". Constants in Go are similar to variables but cannot be reassigned after their initial declaration.
2. `fmt.Println(s)`: Prints the value of the constant `s` to the console.
3. `const n = 500000000`: Declares a constant named `n` and initializes it with the value 500000000.
4. `const d = 3e20 / n`: Declares a constant named `d` and initializes it with the result of the expression `3e20 / n`. The constant `d` is a floating-point number.
5. `fmt.Println(d)`: Prints the value of the constant `d` to the console.
6. `fmt.Println(int64(d))`: Prints the value of `d` after converting it to an int64. This conversion is necessary because `d` is a floating-point number, and `math.Sin` expects an argument of type `float64` or `float32`.
7. `fmt.Println(math.Sin(n))`: Prints the result of the sine function applied to the constant `n` using the `Sin` function from the `math` package.
