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

import static java.util.Arrays.*;

public class Main {
	private static final int mod = (int)1e9+7;

	final Random random = new Random(0);
	final IOFast io = new IOFast();

	/// MAIN CODE
	public void run() throws IOException {
		if (false) {
			final int n = 3;
			for (int i = 0; i < 1<<(n*n); i++) {
				char[][] cs = from(i, n);
				if (fast(n, cs) != naive(n, cs)) {
					dump(cs, fast(n, cs), naive(n, cs));
					throw new RuntimeException();
				}
			}
		}
		
//		int TEST_CASE = Integer.parseInt(new String(io.nextLine()).trim());
		int TEST_CASE = 1;
		while(TEST_CASE-- != 0) {
			int n = io.nextInt();
			char[][] cs = new char[n][];
			for (int i = 0; i < n; i++) {
				cs[i] = io.next();
			}
			io.out.println(fast(n, cs));
		}
	}
	
	int fast(int n, char[][] cs) {
		boolean allW = true;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) allW &= cs[i][j] == '.';
		}
		if (allW) {
			return -1;
		}
		
		int allBlackCol = 0;
		for (int y = 0; y < n; y++) {
			int cnt = 0;
			for (int x = 0; x < n; x++) {
				if (cs[x][y] == '#') { cnt++; }
			}
			if (cnt == n) allBlackCol++;
		}
		int ans = Integer.MAX_VALUE;
		for (int y = 0; y < n; y++) {
			boolean can = false;
			int cnt = 0;
			for (int x = 0; x < n; x++) {
				if (cs[y][x] == '.') { cnt++; }
				if (cs[x][y] == '#') { can = true; }
			}
			if (cnt != n) {
				ans = Math.min(ans, (can ? 0 : 1) + cnt + n - allBlackCol);
			}
		}
		return ans;
	}
	
	int naive(int n, char[][] cs) {
		int bit = 0;
		for (int y = 0, i = 0; y < n; y++) {
			for (int x = 0; x < n; x++, i++) {
				bit |= (cs[y][x] == '.' ? 0 : 1) << i;
			}
		}
		boolean[] vis = new boolean[1<<(n*n)];
		Queue<Integer> que = new ArrayDeque<>();
		que.add(bit);
		vis[bit] = true;
		int cnt = 0;
		while (!que.isEmpty()) {
			cnt++;
			Queue<Integer> next = new ArrayDeque<>();
			while (!que.isEmpty()) {
				int cur = que.poll();
				cs = from(cur, n);
				for (int i = 0; i < n; i++) {
					for (int j = 0; j < n; j++) {
						char[][] cs2 = from(cur, n);
						for (int k = 0; k < n; k++) {
							cs2[k][i] = cs[j][k];
						}
						int t = to(cs2, n);
						if (t+1 == 1<<(n*n)) {
							return cnt;
						}
						if (!vis[t]) {
							vis[t] = true;
							next.add(t);
						}
					}
				}
			}
			que = next;
		}
		return -1;
	}
	
	char[][] from(int cur, int n) {
		char[][] cs = new char[n][n];
		for (int y = 0, i = 0; y < n; y++) {
			for (int x = 0; x < n; x++, i++) {
				cs[y][x] = ".#".charAt(cur >> i & 1);
			}
		}
		return cs;
	}
	
	int to(char[][] cs, int n) {
		int bit = 0;
		for (int y = 0, i = 0; y < n; y++) {
			for (int x = 0; x < n; x++, i++) {
				bit |= (cs[y][x] == '.' ? 0 : 1) << i;
			}
		}
		return bit;
	}
	
	/// TEMPLATE
	static int gcd(int n, int r) { return r == 0 ? n : gcd(r, n%r); }
	static long gcd(long n, long r) { return r == 0 ? n : gcd(r, n%r); }
	
	static <T> void swap(T[] x, int i, int j) { T t = x[i]; x[i] = x[j]; x[j] = t; }
	static void swap(int[] x, int i, int j) { int t = x[i]; x[i] = x[j]; x[j] = t; }

	void printArrayLn(int[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	void printArrayLn(long[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); }
	
	static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); } 
	
	void main() throws IOException {
		//		IOFast.setFileIO("rle-size.in", "rle-size.out");
		try { run(); }
		catch (EndOfFileRuntimeException e) { }
		io.out.flush();
	}
	public static void main(String[] args) throws IOException { new Main().main(); }
	
	static class EndOfFileRuntimeException extends RuntimeException {
		private static final long serialVersionUID = -8565341110209207657L; }

	static
	public class IOFast {
		private BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		private PrintWriter out = new PrintWriter(System.out);

		void setFileIn(String ins) throws IOException { in.close(); in = new BufferedReader(new FileReader(ins)); }
		void setFileOut(String outs) throws IOException { out.flush(); out.close(); out = new PrintWriter(new FileWriter(outs)); }
		void setFileIO(String ins, String outs) throws IOException { setFileIn(ins); setFileOut(outs); }

		private static int pos, readLen;
		private static final char[] buffer = new char[1024 * 8];
		private static char[] str = new char[500*8*2];
		private static boolean[] isDigit = new boolean[256];
		private static boolean[] isSpace = new boolean[256];
		private static boolean[] isLineSep = new boolean[256];

		static { for(int i = 0; i < 10; i++) { isDigit['0' + i] = true; } isDigit['-'] = true; isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true; isLineSep['\r'] = isLineSep['\n'] = true; }
		public int read() throws IOException { if(pos >= readLen) { pos = 0; readLen = in.read(buffer); if(readLen <= 0) { throw new EndOfFileRuntimeException(); } } return buffer[pos++]; }
		public int nextInt() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; int ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; }
		public long nextLong() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; long ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; }
		public char nextChar() throws IOException { while(true) { final int c = read(); if(!isSpace[c]) { return (char)c; } } }
		int reads(int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } if(str.length == len) { char[] rep = new char[str.length * 3 / 2]; System.arraycopy(str, 0, rep, 0, str.length); str = rep; } str[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		int reads(char[] cs, int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } cs[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; }
		public char[] nextLine() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isLineSep); try { if(str[len-1] == '\r') { len--; read(); } } catch(EndOfFileRuntimeException e) { ; } return Arrays.copyOf(str, len); }
		public String nextString() throws IOException { return new String(next()); }
		public char[] next() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); return Arrays.copyOf(str, len); }
//		public int next(char[] cs) throws IOException { int len = 0; cs[len++] = nextChar(); len = reads(cs, len, isSpace); return len; }
		public double nextDouble() throws IOException { return Double.parseDouble(nextString()); }
		public long[] nextLongArray(final int n) throws IOException { final long[] res = new long[n]; for(int i = 0; i < n; i++) { res[i] = nextLong(); } return res; }
		public int[] nextIntArray(final int n) throws IOException { final int[] res = new int[n]; for(int i = 0; i < n; i++) { res[i] = nextInt(); } return res; }
		public int[][] nextIntArray2D(final int n, final int k) throws IOException { final int[][] res = new int[n][]; for(int i = 0; i < n; i++) { res[i] = nextIntArray(k); } return res; }
		public int[][] nextIntArray2DWithIndex(final int n, final int k) throws IOException { final int[][] res = new int[n][k+1]; for(int i = 0; i < n; i++) { for(int j = 0; j < k; j++) { res[i][j] = nextInt(); } res[i][k] = i; } return res; }
		public double[] nextDoubleArray(final int n) throws IOException { final double[] res = new double[n]; for(int i = 0; i < n; i++) { res[i] = nextDouble(); } return res; }
	}
}


Measured memory_bytes: 23636