# Problem 1: Multiples of 3 and 5

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

# Sample 00

input00.txt```
10
```

output00.txt
```
23
```

# Sample 01

input01.txt```
1000
```

output01.txt
```
233168
```

# Solution

`main.go`

```
package main
import (
"fmt"
)
func main() {
var n int
fmt.Scan(&n)
n = n - 1
fmt.Println(SummationBy(n, 3) + SummationBy(n, 5) - SummationBy(n, 15))
}
func Summation(n int) int {
return n * (n + 1) / 2
}
func SummationBy(n, m int) int {
return Summation(n/m) * m
}
```