#include <bits/stdc++.h>
 #define ll long long
 #define ull unsigned long long
 #define pi 3.141592654
 #define NUM 1e18
 #define Mod  1'000'000'007
 #define fixed(n) fixed<<setprecision(n)
 #define cin(v) for(auto &i:v) cin >> i ;
 #define cout(v) for(auto &i:v) cout << i  <<" ";
 #define vowel(x) (x=='e'||x=='a'||x=='i'||x=='o'||x=='u')
 #define small(x) (x>=97&&x<=122)
 #define capital(x) (x>=65&&x<=90)
 #define Tolower(s) transform(s.begin(),s.end(),s.begin(),::tolower);
 #define Toupper(s) transform(s.begin(),s.end(),s.begin(),::toupper);
 #define sz(x) (int)(x.size())
 #define all(v) ((v).begin()), ((v).end())
 #define allr(v) ((v).rbegin()), ((v).rend())
 #define updmax(a,b) a=max(a,b)
 #define updmin(a,b) a=min(a,b)
 #define ceil(a,b) ((a/b)+(a%b?1:0))
 /* asc -> 1 2 3 ,des -> 3 2 1 */

 /***********************************************************************************/
 using namespace std;
 void Rofyda_Elghadban(){
  #ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
   #endif
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
 }

 void solve(){
  int n,m,k,counter1=0,counterdot1=0,mini1=INT_MAX,c1=0,counter2=0,counterdot2=0,mini2=INT_MAX,c2=0;
  cin>>n>>m>>k;
  char arr[n][m];
  for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
      cin>>arr[i][j];
    }
  }
  for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
      if(counter1==k){
        c1++;
      }
      if((arr[i][j]=='.'||arr[i][j]=='o')&&counter1!=k){
        counter1++;
        if(arr[i][j]=='.'){
          counterdot1++;
        }
      }else if((arr[i][j]=='.'||arr[i][j]=='o')&&counter1==k){
        mini1=min(mini1,counterdot1);
        if(arr[i][j-k]=='.'&&arr[i][j]=='.'){
          continue;
        }else{
          counterdot1++;
        }
      }else if(arr[i][j]=='x'){
        if(counter1==k){
          mini1=min(mini1,counterdot1);
          counterdot1=0;
          counter1=0;
        }
      }
    }
    counterdot1=0;
    counter1=0;
  }
  for(int i=0;i<m;i++){
    for(int j=0;j<n;j++){
      if(counter2==k){
        c2++;
      }
      if((arr[j][i]=='.'||arr[j][i]=='o')&&counter2!=k){
        counter2++;
        if(arr[j][i]=='.'){
          counterdot2++;
        }
      }else if((arr[j][i]=='.'||arr[j][i]=='o')&&counter2==k){
        mini2=min(mini2,counterdot2);
        if(arr[j][i-k]=='.'&&arr[j][i]=='.'){
          continue;
        }else{
          counterdot2++;
        }
      }else if(arr[j][i]=='x'){
        if(counter2==k){
          mini2=min(mini2,counterdot2);
          counterdot2=0;
          counter2=0;
        }
      }
    }
    counterdot2=0;
    counter2=0;
  }
  if(c1==0&&c2==0){
    cout<<-1<<"\n";
    return;
  }
  cout<<min(mini1,mini2)<<"\n";
 }

 int main(){
  Rofyda_Elghadban();
  // int t;
  // cin>>t;
  // while(t--){
  //   solve();
  // }
  solve();
  return 0;
 }