#include <cstdio>
#include <iostream>
#include <vector>
#include <deque>
#include <cmath>
#include <iomanip>
#include <algorithm>
using namespace std;

const int MAXN = 35;
const int dx[4] = {0, 1, 0, -1};
const int dy[4] = {1, 0, -1, 0};

int n, m, T;
char grid[MAXN][MAXN];

bool isValid(int x, int y) {
    return x >= 0 && x < n && y >= 0 && y < m;
}

vector<vector<int>> bfs01(int sx, int sy) {
    vector<vector<int>> dist(n, vector<int>(m, 0x3f3f3f3f));
    vector<vector<bool>> visited(n, vector<bool>(m, false));
    deque<pair<int, int>> dq;
    
    int startcost = (grid[sx][sy] == '1') ? 1 : 0;
    dist[sx][sy] = startcost;
    dq.push_back({sx, sy});
    
    while (!dq.empty()) {
        auto [x, y] = dq.front();
        dq.pop_front();
        
        if (visited[x][y]) continue;
        visited[x][y] = true;
        
        for (int i = 0; i < 4; i++) {
            int nx = x + dx[i];
            int ny = y + dy[i];
            
            if (!isValid(nx, ny)) continue;
            
            int cost = (grid[nx][ny] == '1') ? 1 : 0;
            if (dist[x][y] + cost < dist[nx][ny]) {
                dist[nx][ny] = dist[x][y] + cost;
                if (cost == 0) {
                    dq.push_front({nx, ny});
                } else {
                    dq.push_back({nx, ny});
                }
            }
        }
    }
    
    return dist;
}

double euladis(int x1, int y1, int x2, int y2) {
    return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    cin >> n >> m >> T;
    
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> grid[i][j];
        }
    }
    
    double maxdis = 0.0;
    
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            auto dist = bfs01(i, j);
            for (int x = 0; x < n; x++) {
                for (int y = 0; y < m; y++) {
                    if (dist[x][y] <= T) {
                        maxdis = max(maxdis, euladis(i, j, x, y));
                    }
                }
            }
        }
    }
    printf("%.6f\n", maxdis);
}