#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <unordered_set>

using namespace std;

const int nMax = 305;
const int mMax = 305;
const int dx[] = {-1, 1, 0, 0};
const int dy[] = {0, 0, -1, 1};

ofstream out("zone2.out");

struct zona
{
    int marime;
    unordered_set<int> vecini;
};

int n, m, k;
char a[nMax][mMax];
int zonaId[nMax][mMax];
zona zone[nMax*mMax];
bool deleted[nMax*mMax];
bool viz[nMax][mMax];
int nrZone;
int rasp;

void citire()
{
    ifstream in("zone2.in");
    in >> n >> m >> k;
    for(int i = 1; i <= n; ++i)
        in >> (a[i]+1);
    in.close();
}

int CreateZone(int startX, int startY)
{
    int ret = 1;
    queue<pair<int, int> > q;
    q.push(make_pair(startX, startY));
    zonaId[startX][startY] = nrZone;

    int newx, newy;
    pair<int, int> p;
    while(q.empty() == false)
    {
        p = q.front();
        q.pop();

        for(int d = 0; d < 4; ++d)
        {
            newx = p.first + dx[d];
            newy = p.second + dy[d];

            if(a[newx][newy] == a[startX][startY] && zonaId[newx][newy] == 0)
            {
                zonaId[newx][newy] = nrZone;
                q.push(make_pair(newx, newy));
                ret++;
            }
        }
    }
    return ret;
}

void SetVecini(int startX, int startY)
{
    queue<pair<int, int> > q;
    q.push(make_pair(startX, startY));
    viz[startX][startY] = true;

    int newx, newy;
    pair<int, int> p;
    while(q.empty() == false)
    {
        p = q.front();
        q.pop();
        for(int d = 0; d < 4; ++d)
        {
            newx = p.first + dx[d];
            newy = p.second + dy[d];
            if(newx < 1 || newx > n || newy < 1 || newy > m)
                continue;
            if(zonaId[newx][newy] == zonaId[startX][startY])
            {
                if(viz[newx][newy] == false)
                {
                    q.push(make_pair(newx, newy));
                    viz[newx][newy] = true;
                }
            }
            else
                zone[zonaId[startX][startY]].vecini.insert(zonaId[newx][newy]);

        }
    }
}

void DeleteZone(int ind)
{
    if(deleted[ind] == true)
        return;
    rasp -= zone[ind].marime;
    deleted[ind] = true;
    for(auto v:zone[ind].vecini)
    {
        zone[v].vecini.erase(ind);
        if(zone[v].vecini.size() < k)
            DeleteZone(v);
    }
    zone[ind].vecini.clear();
}

void rezolvare()
{
    rasp = n * m;
    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= m; ++j)
            if(zonaId[i][j] == 0)
                zone[++nrZone].marime = CreateZone(i, j);

    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= m; ++j)
            if(zone[zonaId[i][j]].vecini.size() == 0)
                SetVecini(i, j);
    bool ok = true;
    while(ok)
    {
        ok = false;
        for(int i = 1; i <= nrZone; ++i)
        {
            if(deleted[i] == false && zone[i].vecini.size() < k)
            {
                ok = true;
                DeleteZone(i);
            }
        }
    }
    out << rasp;
}

int main()
{
    citire();
    rezolvare();
    return 0;
}