#include<cstdio>

 #include<cstring>

 #include<cstdlib>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 struct node

 {

     int x,y,next;

 }a[];int len,last[];

 void ins(int x,int y)

 {

     len++;a[len].x=x;a[len].y=y;

     a[len].next=last[x];last[x]=len;

 }

 char s[][];

 int n,m,R,C,t;

 int match[],chw[];

 bool findmuniu(int x)

 {

     for(int k=last[x];k;k=a[k].next)

     {

         int y=a[k].y;

         if(chw[y]!=t)

         {

             chw[y]=t;

             if(match[y]== || findmuniu(match[y]))

             {

                 match[y]=x;

                 return true;

             }

         }

     }

     return false;

 }

 int d[][];//辣鸡数据

 int main()

 {

     scanf("%d%d%d%d",&n,&m,&R,&C);

     for(int i=;i<=n;i++)scanf("%s",s[i]+);

     int ss=;memset(d,-,sizeof(d));

     for(int i=;i<=n;i++)for(int j=;j<=m;j++)d[i][j]=++ss;

     const int dx[]={,R,R,C,C};

     const int dy[]={,-C,C,-R,R};

     int sum=;len=;memset(last,,sizeof(last));

     for(int i=;i<=n;i++)

         for(int j=;j<=m;j++)

             if(s[i][j]=='.')

             {

                 sum++;

                 for(int k=;k<=;k++)

                 {

                     int x=i+dx[k],y=j+dy[k];

                     if(d[x][y]!=- && s[x][y]!='x')

                         ins(d[i][j],d[x][y]+n*m);

                 }

             }

     memset(match,,sizeof(match));

     memset(chw,,sizeof(chw));

     int ans=;

     for(int i=;i<=n;i++)

         for(int j=;j<=m;j++)

             if(s[i][j]=='.')

             {

                 t++;

                 if(findmuniu(d[i][j]))ans++;

             }

     printf("%d\n",sum-ans);

     return ;

 }