#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pr pair<ll, ll>
#define f first
#define s second
#define pb push_back
const int ndim=4001;
int ns;
vector<vector<int>> d(ndim, vector<int>(ndim));
void floodfill(int x, int y, int h, int w, int col){
// out of bound
// count & change color
ns++; d[x][y]^=1;
if(x==h-1 && y==w-1) return;
int dx[4]={1, -1, 0, 0};
int dy[4]={0, 0, 1, -1};
for (int i=0; i<4; i++){
int x1=x+dx[i]; int y1=y+dy[i];
if(x1>=0 && x1<h && y1>=0 && y1<w){
if(d[x1][y1]==col) {
floodfill(x1, y1, h, w, col);
}
}
}
}
int main(){
int h, w; cin>>h>>w;
//vector<vector<int>> d(h, vector<int> (w, -1));
int nf=0;
for (int i=0; i<h; i++){
string s; cin>>s;
for (int j=0; j<w; j++){
if(s[j]=='.') {
d[i][j]=-1; continue;
}
nf++;
if(s[j]=='R') d[i][j]=0;
else d[i][j]=1;
}
}
//for (int i=0; i<h; i++){
// for (int j=0; j<w; j++) cout<<d[i][j]<<" ";
// cout<<endl;
//}
ns=0;
int cnt=0;
while(ns<nf){
ns=0; cnt++;
floodfill(0, 0, h, w, d[0][0]);
if(ns==nf) break;
}
cout<<cnt<<endl;
}
