#include <iostream>
#include <vector>
#include <set>
#include <unordered_set>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <numeric>
#include <queue>
#include <iomanip>
#include <numeric>
#include <cmath>
using namespace std;

int main() {
	int n, k;
	cin >> n >> k;
	unordered_map<int, int> um;
	for (int i = 0; i < n; i++) {
		int t;
		cin >> t;
		um[t]++;
	}
	int res = 0;
	for (int i = 0; i < k; i++) {
		int index = 0;
		while (um[index] > 0) {
			um[index]--;
			index++;
		}
		res += index;
	}
	cout << res << endl;
}





//#define _GLIBCXX_DEBUG
//#include "atcoder/all"
//using namespace atcoder;
#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define Dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) (((n) >> (k)) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
bool dbg = true;
}  // namespace mydef
using namespace mydef;
#define pb push_back
//#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
//#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define asn ans

int H, W;
vector<string> S;

void solve() {
    auto check = [&](int i, int j) {
        return (S[i][j] + S[i][j + 1] + S[i + 1][j] + S[i + 1][j + 1]) % 2 == 1;
    };

    int ans = 0;
    for (int i = 0; i < H - 1; i++) {
        for (int j = 0; j < W - 1; j++) {
            ans += check(i, j);
        }
    }
    cout << ans << endl;
}

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

    cin >> H >> W;
    S.resize(H);
    for (int i = 0; i < H; i++) {
        cin >> S[i];
        for (auto& c : S[i])
            c = c == '#';
    }

    solve();
    return 0;
}
