int n,m,k,mini1=INT_MAX,mini2=INT_MAX;
  cin>>n>>m>>k;
  char arr1[n][m];
  int arr[n][m];
  for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
      cin>>arr1[i][j];
      if(arr1[i][j]=='.'){
        arr[i][j]=0;
      }else if(arr1[i][j]=='o'){
        arr[i][j]=1;
      }else if(arr1[i][j]=='x'){
        arr[i][j]=-1;
      }
    }
  }
  map<int,int>mp;
  for(int i=0;i<n;i++){
    for(int j=0;j<m;j++){
      if(arr[i][j]==0){
        mp[0]++;
      }else if(arr[i][j]==1){
        mp[1]++;
      }else if(arr[i][j]==-1&&(mp[0]+mp[1]==k)){
        mini1=min(mini1,mp[0]);
        mp[1]=0;
        mp[0]=0;
      }else if(arr[i][j]==-1&&(mp[0]+mp[1]!=k)){
        mp[1]=0;
        mp[0]=0;
      }
      if(mp[0]+mp[1]==k){
        mini1=min(mini1,mp[0]);
      }else if((arr[i][j]=='0'||arr[i][j]=='1')&&mp[0]+mp[1]==k){
        if(j-k>=0&&(arr[i][j-k]=='0'&&arr[i][j]=='0')){
          continue;
        }else if(j-k>=0&&(arr[i][j-k]=='1'&&arr[i][j]=='0')){
          mp[0]++;
          mp[1]--;
        }else if(j-k>=0&&(arr[i][j-k]=='1'&&arr[i][j]=='1')){
          continue;
        }else if(j-k>=0&&(arr[i][j-k]=='0'&&arr[i][j]=='1')){
          mp[0]--;
          mp[1]++;
        }
        mini1=min(mini1,mp[0]);
      }
    }
    mp[0]=0;
    mp[1]=0;
  }
  cout<<mini1<<"\n";