#include <bits/stdc++.h>
using namespace std;

using vi = vector<int>;

struct UnionFind {
	vi par, rank, size; int c;
	UnionFind(int n) : par(n), rank(n,0), size(n,1), c(n) {
		for (int i = 0; i < n; ++i) par[i] = i;
	}

	int find(int i) { return (par[i] == i ? i : (par[i] = find(par[i]))); }
	bool same(int i, int j) { return find(i) == find(j); }
	int get_size(int i) { return size[find(i)]; }
	int count() { return c; }
	void purge(int i) { size[i] = 0; }

	void merge(int i, int j) {
		if ((i = find(i)) == (j = find(j))) return;
		c--;
		if (rank[i] > rank[j]) swap(i, j);
		par[i] = j; size[j] += size[i];
		if (rank[i] == rank[j]) rank[j]++;
	}
};

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int h, n, m;
	cin >> h >> n >> m;

	UnionFind uf(n * m);
	vector<char> prow(m, '#');
	for (int i = 0; i < n; ++i) {
		vector<char> row(m);
		for (int j = 0; j < m; ++j) {
			cin >> row[j];
			if (row[j] == '#')
				uf.purge(i * m + j);
			else {
				if (j > 0 && row[j - 1] == '.')
					uf.merge(i * m + j, i * m + j - 1);
				if (i > 0) {
					if (prow[j] == '.')
						uf.merge(i * m + j, (i - 1) * m + j);
					if (i % 2 == 0 && j > 0 && prow[j-1] == '.')
						uf.merge(i * m + j, (i - 1) * m + j - 1);
					if (i % 2 == 1 && j + 1 < m && prow[j+1] == '.')
						uf.merge(i * m + j, (i - 1) * m + j + 1);
				}
			}
		}
		prow = row;
	}

	vi sz;
	for (int i = 0; i < n*m; ++i)
		if (uf.find(i) == i)
			sz.push_back(uf.get_size(i));

	sort(sz.rbegin(), sz.rend());
	sz.insert(sz.begin(), 0);
	partial_sum(sz.begin(), sz.end(), sz.begin());
	cout << int(lower_bound(sz.begin(), sz.end(), h) - sz.begin()) << endl;

	return 0;
}