#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define drep(i,j,n) for(int i=0;i<(int)(n-1);i++)for(int j=i+1;j<(int)(n);j++)
#define trep(i,j,k,n) for(int i=0;i<(int)(n-2);i++)for(int j=i+1;j<(int)(n-1);j++)for(int k=j+1;k<(int)(n);k++)
#define codefor int test;scanf("%d",&test);while(test--)
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define yes(ans) if(ans)printf("yes\n");else printf("no\n")
#define Yes(ans) if(ans)printf("Yes\n");else printf("No\n")
#define YES(ans) if(ans)printf("YES\n");else printf("NO\n")
#define vector1d(type,name,...) vector<type>name(__VA_ARGS__)
#define vector2d(type,name,h,...) vector<vector<type>>name(h,vector<type>(__VA_ARGS__))
#define vector3d(type,name,h,w,...) vector<vector<vector<type>>>name(h,vector<vector<type>>(w,vector<type>(__VA_ARGS__)))
#define umap unordered_map
#define uset unordered_set
using namespace std;
using ll = long long;
const int MOD=1000000007;
const int MOD2=998244353;
const int INF=1<<30;
const ll INF2=(ll)1<<60;
//入力系
void scan(int& a){scanf("%d",&a);}
void scan(long long& a){scanf("%lld",&a);}
template<class T,class L>void scan(pair<T, L>& p){scan(p.first);scan(p.second);}
template<class T> void scan(T& a){cin>>a;}
template<class T> void scan(vector<T>& vec){for(auto&& it:vec)scan(it);}
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail){scan(head);in(tail...);}
//出力系
void print(const int& a){printf("%d",a);}
void print(const long long& a){printf("%lld",a);}
void print(const double& a){printf("%.15lf",a);}
template<class T,class L>void print(const pair<T, L>& p){print(p.first);putchar(' ');print(p.second);}
template<class T> void print(const T& a){cout<<a;}
template<class T> void print(const vector<T>& vec){if(vec.empty())return;print(vec[0]);for(auto it=vec.begin();++it!= vec.end();){putchar(' ');print(*it);}}
void out(){putchar('\n');}
template<class T> void out(const T& t){print(t);putchar('\n');}
template <class Head, class... Tail> void out(const Head& head,const Tail&... tail){print(head);putchar(' ');out(tail...);}
//デバッグ系
template<class T> void dprint(const T& a){cerr<<a;}
template<class T> void dprint(const vector<T>& vec){if(vec.empty())return;cerr<<vec[0];for(auto it=vec.begin();++it!= vec.end();){cerr<<" "<<*it;}}
void debug(){cerr<<endl;}
template<class T> void debug(const T& t){dprint(t);cerr<<endl;}
template <class Head, class... Tail> void debug(const Head& head, const Tail&... tail){dprint(head);cerr<<" ";debug(tail...);}
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
ll updivide(ll a,ll b){if(a%b==0) return a/b;else return (a/b)+1;}
template<class T> void chmax(T &a,const T b){if(b>a)a=b;}
template<class T> void chmin(T &a,const T b){if(b<a)a=b;}

int main(){
    LL(n,m);
    if(n==m){
        out(0);
        return 0;
    }
    if(m==0){
        out(1);
        return 0;
    }
    vector<ll> vec(m);
    in(vec);
    sort(all(vec));
    ll l=1,r=n,mid,ans=INF2,pre,d;
    bool h=false;
    while(l<r){
        mid=(l+r)/2;
        h=true;
        pre=0;
        d=0;
        for(int i=0;i<m;i++){
            if(vec[i]-pre-1>=mid){
                d+=updivide(vec[i]-pre-1,mid);
            }else{
                if(vec[i]-pre!=1){
                    h=false;
                }
            }
            pre=vec[i];
        }
        if(n-vec[m-1]>=mid){
            d+=updivide(n-vec[m-1],mid);
        }else{
            if(n+1-vec[m-1]!=1){
                h=false;
            }
        }
        if(h){
            l=mid+1;
            chmin(ans,d);
        }else{
            r=mid;
        }
    }      
    out(ans);
}
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

constexpr int N = 1005;

int n, m;
std::string s;
int f[N << 1];
std::vector<int> a, b;

int find(int x) {
    if (x != f[x]) f[x] = find(f[x]);
    return f[x];
}

inline void merge(int x, int y) { f[find(x)] = find(y); }

int main() {
    std::ios::sync_with_stdio(false), std::cin.tie(nullptr);
    std::cin >> n >> m;
    for (int i = 1; i <= n + m; ++i) f[i] = i;
    for (int i = 1; i <= n; ++i) {
        std::cin >> s;
        for (int j = 1; j <= m; ++j)
            if (s[j - 1] == '#')
                merge(i, j + n);
    }
    merge(1, n + 1);
    merge(1, n + m);
    merge(n, n + 1);
    merge(n, n + m);
    for (int i = 1; i <= n; ++i) a.push_back(find(i));
    for (int i = 1; i <= m; ++i) b.push_back(find(i + n));
    std::sort(a.begin(), a.end());
    std::sort(b.begin(), b.end());
    std::cout << std::min(std::unique(a.begin(), a.end()) - a.begin(), std::unique(b.begin(), b.end()) - b.begin()) - 1 << '\n';
    return 0;
}
