package main

import (
	"fmt"
)

func main() {
	var n int
	fmt.Scan(&n)
	var s string
	fmt.Scan(&s)

	totalL, totalO := 0, 0
	for i := 0; i < n; i++ {
		if s[i] == 'L' {
			totalL++
		} else {
			totalO++
		}
	}

	leftL, leftO := 0, 0
	for k := 1; k < n; k++ {
		if s[k-1] == 'L' {
			leftL++
		} else {
			leftO++
		}
		rightL := totalL - leftL
		rightO := totalO - leftO

		if leftL != rightL && leftO != rightO {
			fmt.Println(k)
			return
		}
	}
	fmt.Println("-1")
}