#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pll = pair<long long, long long>;
constexpr char ln =  '\n';
constexpr long long MOD = 1000000007;
constexpr long long INF = 1000000000 + 100;
constexpr long long LINF = 1000000000000000000 + 100;
#define all(v) v.begin(), v.end()
#define rep(i, n) for(int i=0;i<(n);i++)
#define rept(i, j, n) for(int i=(j); i<(n); i++)
#define rrep(i, n) for(int i=(n); i>=0; i--)
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

int dx[4] = {0,1,0,1};
int dy[4] = {0,0,1,1};

int main(){
    int H, W; cin >> H >> W;
    vector<string> g(H); rep(i, H)cin >> g[i];

    int res = 0;
    rep(i, H-1){
        rep(j, W-1){
            int b = 0;
            rep(k, 4)if(g[i+dy[k]][j+dx[k]]=='#')b++;
            if(b%2==1)res++;
        }
    }
    cout << res << ln;
}

#include <bits/stdc++.h>
using namespace std;
#define ALL(x) (x).begin(),(x).end()
#define COUT(x) cout<<(x)<<"\n"
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define REP(i,n) for(int i=0;i<n;i++)
#define YES(x) cout<<(x?"YES":"NO")<<"\n"
#define Yes(x) cout<<(x?"Yes":"No")<<"\n"
#define dump(x) cout<<#x<<" = "<<(x)<<"\n"
#define endl "\n"
using G = vector<vector<int>>;
using M = map<int,int>;
using P = pair<int,int>;
using PQ = priority_queue<int>;
using PQG = priority_queue<int,vector<int>,greater<int>>;
using V = vector<int>;
using ll = long long;
using edge = struct { int to; int cost; };
template<class T>bool chmax(T &a,const T &b) {if(a<b){a=b; return 1;} return 0;}
template<class T>bool chmin(T &a,const T &b) {if(b<a){a=b; return 1;} return 0;}
const int INF = 1e9;
const int MOD = 1e9+7;
const ll LINF = 1e18;

int main() {
  IOS;
  string a,b;
  cin >> a >> b;
  int suma=0,sumb=0;
  REP(i,a.size()) {
    suma += a[i] - '0';
  }
  REP(i,b.size()) {
    sumb += b[i] - '0';
  }
  COUT(max(suma, sumb));

  return 0;
}