Baekjoon #25427

#include<bits/stdc++.h>

using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N; cin >> N;
    vector<long long> DP(5);
    string S; cin >> S;
    string K = "DKSH";
    DP[0] = 1;
    for(int i = 0; i < N; ++i) {
        int idx = -1;
        for(int j = 0; j < 4; ++j) {
            if(K[j] == S[i]) {
                idx = j + 1;
                break;
            }
        }
        if(idx != -1) DP[idx] += DP[idx - 1];
    }
    cout << DP[4];

    return 0;
}

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

public class Main{
    static String DKSH = "DKSH";
	public static void main(String[] args){
        FastReader rd = new FastReader();

        int N = rd.nextInt();
        String S = rd.next();
        long[] DP = new long[5];

        DP[0] = 1;
        for(int i = 1; i <= N; ++i) {
            int idx = get_index(S.charAt(i - 1));
            if(idx > 0) {
                DP[idx] += DP[idx - 1];
            }
        }

        System.out.print(DP[4]);
	}

    static public int get_index(char ch) {
        for(int i = 0; i < 4; ++i) {
            if(DKSH.charAt(i) == ch) return i + 1;
        }
        return 0;
    }

    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();
            }
            return str;
        }
    }
}