#include<bits/stdc++.h>
#define int long long
using namespace std;
#define For(i,a,b) for(int i = a; i <= b; ++i)
int Map[300][300];
int n,m,c,d;
int Row[300],Col[300];
int maxx = 0;
    int cnt = 0;

int value(){
    maxx = 0;
    For(i,1,n) maxx = max(maxx,Row[i]);
    For(j,1,m) maxx = max(maxx,Col[j]);
    return maxx * c;
}
void del(int x,int y){
    Row[x] --;
    Col[y] --;
    Map[x][y] = 0;
    value();
    --cnt;
}
signed main(){
#ifdef NICEGUODONG
    freopen("data.in","r",stdin);
#endif
    ios::sync_with_stdio(false);
    
    cin >> n >> m >> c >>d;
    For(i,1,n) For(j,1,m){
        char tmp;
        cin >> tmp;
        if(tmp == '.'){
            Map[i][j] = 1;
            ++cnt;
            Row[i]++;
            Col[j]++;
        }
    }
    int ans = value();
    int num = 0;
    do{
        int flag = 0;
        ++num;
        For(i,1,n){
            if(flag) break;
            if(Row[i] == maxx){
                flag = 1;
                int maxv = 0,pos = -1;
                For(j,1,m){
                    if(Col[j] >= maxv){
                        pos =j;
                        maxv = Col[j];
                    }
                }
                del(i,pos);
            }
        }        
        if(!flag){
            For(j,1,m){
                if(flag) break;
                if(Col[j] == maxx){
                    flag = 1;
                    int maxv = 0,pos = -1;
                    For(i,1,n){
                        if(Row[i] >= maxv){
                            pos = i;
                            maxv = Row[i];
                        }
                    }
                    del(pos,j);
                }
            }        
        }
        ans = min(ans,maxx * c + num * d);
    }while(cnt != 0);
    cout << ans << '\n';
    return 0;
}