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

public class Solution {
    Scanner in = new Scanner(new InputStreamReader(System.in));
    PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));

    private void solution() throws IOException {
        int n = in.nextInt();
        int m = in.nextInt();
        String[] grid = new String[n];
        for (int i = 0; i < n; ++i) {
            grid[i] = in.next();
        }
        int[] v = new int[n];
        for (int i = 0; i < n; ++i) {
            int nmask = 0;
            for (int j = 0; j < m; ++j) {
                if (grid[i].charAt(j) == '*') {
                    nmask = nmask | (1 << j);
                }
            }
            v[i] = nmask;
        }
        int firstLength = n / 2;
        int secondLength = (n + 1) / 2;
        int[] first = new int[1 << firstLength];
        int[] second = new int[1 << secondLength];
        for (int mask = 0; mask < (1 << firstLength); ++mask) {
            int curMask = 0;
            for (int i = 0; i < firstLength; ++i) {
                if (((mask >> i) & 1) == 1) {
                    curMask |= v[i];
                }
            }
            first[mask] = curMask;
        }
        for (int mask = 0; mask < (1 << secondLength); ++mask) {
            int curMask = 0;
            for (int i = 0; i < secondLength; ++i) {
                if (((mask >> i) & 1) == 1) {
                    curMask |= v[n / 2 + i];
                }
            }
            second[mask] = curMask;
        }

        int res = Integer.MAX_VALUE;
        for (int mask = 0; mask < (1 << n); ++mask) {
            int a = Integer.bitCount(mask);
            int firstMask = first[((1 << firstLength) - 1) ^ (mask & ((1 << firstLength) - 1))];
            int secondMask = second[((1 << secondLength) - 1) ^ (mask >> firstLength)];
            int b = Integer.bitCount(firstMask | secondMask);
            res = Math.min(res, Math.max(a, b));
        }
        out.println(res);
        out.flush();
    }

    private class Scanner {
        BufferedReader reader;
        StringTokenizer tokenizer;

        public Scanner(Reader reader) {
            this.reader = new BufferedReader(reader);
            tokenizer = new StringTokenizer("");
        }

        public boolean hasNext() throws IOException {
            while (!tokenizer.hasMoreTokens()) {
                String line = reader.readLine();
                if (line == null) {
                    return false;
                }
                tokenizer = new StringTokenizer(line);
            }
            return true;
        }

        public String nextLine() throws IOException {
            tokenizer = new StringTokenizer("");
            return reader.readLine();
        }

        public String next() throws IOException {
            hasNext();
            return tokenizer.nextToken();
        }

        public int nextInt() throws IOException, NumberFormatException {
            return Integer.parseInt(next());
        }

    }

    public static void main(String[] args) throws IOException {
        new Solution().solution();
    }
}