import java.io.*;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.*;
import java.util.StringTokenizer;
import java.util.function.BiFunction;
import java.util.function.BinaryOperator;
import java.util.function.ToIntBiFunction;

public class Mark {

    public static void main(String[] args) throws IOException {
        FastReader fr = new FastReader();
        PrintWriter pw = new PrintWriter(System.out);

        int R = fr.nextInt(), C = fr.nextInt();
        if (R == 1 || C == 1) {pw.println(0); pw.close(); return; }
        int ans = 0;
        char[] map = fr.next().toCharArray();
        ans += solve(map);
        for (int i = 0; i < map.length; ++i)
            map[i] = map[i] == 'D' ? 'R' : 'D';
        ans += solve(map);
        pw.println(ans);

        pw.close();
    }

    static int solve(char[] map)
    {
        List<Integer> grab = new ArrayList<>();
        int i = 0;
        while (map[i] == 'D')
            i++;
        int cnt = 0;
        for (; i < map.length; ++i) {
            cnt++;
            if (i == map.length-1 || map[i+1] != map[i]) {
                grab.add(cnt);
                cnt = 0;
            }
        }
        if (grab.size() % 2 == 1)
            grab.add(0);
        int[] prefix = new int[grab.size() / 2], suffix = new int[grab.size() / 2];
        for (i = 0; i < prefix.length; ++i) {
            int j = suffix.length - 1 - i;
            prefix[i] = grab.get(i*2)   + (i>0 ? prefix[i-1] : 0);
            suffix[j] = grab.get(j*2+1) + (i>0 ? suffix[j+1] : 0);
        }
        int min = Math.min(suffix[0], prefix[prefix.length-1]);
        for (i = 0; i < prefix.length-1; ++i)
            min = Math.min(min, prefix[i] + suffix[i+1]);
        return min;
    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            st = null;
            return str;
        }
    }

}