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

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        char[] inputs = sc.next().toCharArray();
        int[] cCounts = new int[3];
        int[] oCounts = new int[3];
        int[] nCounts = new int[3];
        for (int i = 0; i < n * 3; i++) {
            if (inputs[i] == 'c') {
                cCounts[i % 3]++;
            } else if (inputs[i] == 'o') {
                oCounts[i % 3]++;
            } else if (inputs[i] == 'n') {
                nCounts[i % 3]++;
            }
        }
        int ans = 0;
        for (int i = 0; i < 3; i++) {
            ans += Math.min(cCounts[i], Math.min(oCounts[(i + 1) % 3], nCounts[(i + 2) % 3]));
        }
        System.out.println(ans);
    }
}
    
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}