// ~~ icebear ~~
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
template<class T>
bool minimize(T &a, const T &b) {
if (a > b) return a = b, true;
return false;
}
template<class T>
bool maximize(T &a, const T &b) {
if (a < b) return a = b, true;
return false;
}
#define FOR(i,a,b) for(int i=(a); i<=(b); ++i)
#define FORR(i,a,b) for(int i=(a); i>=(b); --i)
#define REP(i, n) for(int i=0; i<(n); ++i)
#define RED(i, n) for(int i=(n)-1; i>=0; --i)
#define MASK(i) (1LL << (i))
#define BIT(S, i) (((S) >> (i)) & 1)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define task "icebear"
/*END OF TEMPLATE. ICEBEAR AND THE CAT WILL WIN VOI26 */
const int MOD = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const ll INF = 1e18 + 27092008;
const int N = 1000 + 5;
int n, m, f[N][15][MASK(10)];
char a[N][15];
void init(void) {
cin >> n >> m;
REP(i, n) REP(j, m) cin >> a[i][j];
}
void process(void) {
memset(f, 0x3f, sizeof f);
f[0][0][0] = 0;
REP(i, n) REP(j, m) {
REP(mask, MASK(m)) if (f[i][j][mask] != inf) {
if (a[i][j] == '#') {
// col
if (BIT(mask, j)) {
minimize(f[i][j + 1][mask], f[i][j][mask]);
} else {
minimize(f[i][j + 1][mask | MASK(j)], f[i][j][mask] + 1);
}
int off = min(mask, (int)(mask ^ MASK(j)));
// row
if (j > 0 && a[i][j - 1] == '#' && BIT(mask, j - 1) == 0) {
minimize(f[i][j + 1][off], f[i][j][mask]);
} else {
minimize(f[i][j + 1][off], f[i][j][mask] + 1);
}
} else {
int off = min(mask, (int)(mask ^ MASK(j)));
minimize(f[i][j + 1][off], f[i][j][mask]);
}
}
REP(mask, MASK(m)) f[i + 1][0][mask] = f[i][m][mask];
}
int ans = inf;
REP(mask, MASK(m)) minimize(ans, f[n][0][mask]);
cout << ans;
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
int tc = 1;
// cin >> tc;
while(tc--) {
init();
process();
}
return 0;
}
