#include <bits/stdc++.h>
using namespace std;
const int maxn = 1001;
const int maxm = 11;
int dp[maxn][maxm][(1 << maxm)][2];
bool ready[maxn][maxm][(1 << maxm)][2];
vector <string> grid;
int n, m;
// dp[i][j][mask][is the last square covered by a piece of horizontal tape or not]
// in mask: 1 is if the square is covered by vertical tape
// in mask: 0 is if the square is not covered by vertical tape
int solve(int i, int j, int mask, bool horizontal) {
if (i >= n)
return 0;
if (ready[i][j][mask][horizontal])
return dp[i][j][mask][horizontal];
int ans = 1e9;
if (grid[i][j] == '#') { // closed window
int mask2 = mask;
if (horizontal) {
// continue the horizontal tape
mask2 = (mask2 << 1);
mask2 &= ((1 << m) - 1);
if (j+1 < m)
ans = min(ans, solve(i, j+1, mask2, true));
else
ans = min(ans, solve(i+1, 0, mask2, false));
}
// see if the vertical piece can be continued
mask2 = mask;
mask2 = (mask2 << 1);
if (mask2 & (1 << m)) {
mask2 &= ((1 << m) - 1);
mask2++;
if (j+1 < m)
ans = min(ans, solve(i, j+1, mask2, false));
else
ans = min(ans, solve(i+1, 0, mask2, false));
}
// start a vertical piece
mask2 = mask;
mask2 = (mask2 << 1);
mask2 &= ((1 << m) - 1);
mask2++;
if (j+1 < m)
ans = min(ans, solve(i, j+1, mask2, false) + 1);
else
ans = min(ans, solve(i+1, 0, mask2, false) + 1);
// start a horizontal piece
mask2 = mask;
mask2 = (mask2 << 1);
mask2 &= ((1 << m) - 1);
if (j+1 < m)
ans = min(ans, solve(i, j+1, mask2, true) + 1);
else
ans = min(ans, solve(i+1, 0, mask2, false) + 1);
} else { // open window
int mask2 = mask;
mask2 = (mask2 << 1);
mask2 &= ((1 << m) - 1);
if (j+1 < m)
ans = min(ans, solve(i, j+1, mask2, false));
else
ans = min(ans, solve(i+1, 0, mask2, false));
}
dp[i][j][mask][horizontal] = ans;
ready[i][j][mask][horizontal] = true;
return ans;
}
int main() {
cin >> n >> m;
grid.resize(n+1);
for (int i = 0; i < n; i++)
cin >> grid[i];
cout << solve(0, 0, 0, 0) << '\n';
}
