import java.io.*;
import java.util.*;

public class Solution {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        String order = sc.next();
        char steps[]= order.toCharArray();
        if(n>order.length()){
            System.out.println(-1);
            System.exit(1);
        }
        int valley=0,mountain =0,counter =0;
        for(int i=0;i< n ;i++){
            if(counter ==0){
                if(steps[i]=='U'){
                    mountain++;
                    counter++;
                }
                else{
                    valley++;
                    counter--;
                }
            }
            else{
                if(steps[i]=='U'){
                    counter++;
                }
                else{
                    counter--;
                }
            }
        }
        System.out.println(valley);
        System.exit(0);
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
    }
}