/**************************************************************
    Problem: 1295
    User: BLADEVIL
    Language: C++
    Result: Accepted
    Time:4572 ms
    Memory:3944 kb
****************************************************************/
 
//By BLADEVIL
#include <cmath>
#include <cstdio>
#include <cstring>
#define maxn 400
 
using namespace std;
 
int n,m,T;
char s[maxn];
int map[maxn][maxn],quex[maxn*maxn],quey[maxn*maxn],dis[maxn][maxn],flag[maxn][maxn];
int go[5][2];
double ans;
 
double max(double a,double b) {
    if (a>b) return a; else return b;
}
 
int main() {
    go[1][0]=go[4][1]=-1; go[2][1]=go[3][0]=1;
    scanf("%d%d%d",&n,&m,&T);
    for (int i=1;i<=n;i++) {
        scanf("%s",s+1);
        for (int j=1;j<=m;j++) map[i][j]=s[j]!=‘0‘?1:0;
    }
    for (int i=1;i<=n;i++)
        for (int j=1;j<=m;j++) {
            memset(dis,127,sizeof dis);
            memset(flag,0,sizeof flag);
            quex[1]=i; quey[1]=j; dis[i][j]=(map[i][j]==1);
            int h(0),t(1);
            while (h<t) {
                h=(h%2000)+1;
                int curx(quex[h]),cury(quey[h]);
                flag[curx][cury]=0;
                for (int k=1;k<=4;k++) {
                    int nx(curx+go[k][0]),ny(cury+go[k][1]);
                    if ((nx<1)||(nx>n)||(ny<1)||(ny>m)) continue;
                    if (dis[curx][cury]+(map[nx][ny]==1)<dis[nx][ny]) {
                        dis[nx][ny]=dis[curx][cury]+(map[nx][ny]==1);
                        if (!flag[nx][ny]) {
                            t=(t%2000)+1; 
                            quex[t]=nx; quey[t]=ny;
                            flag[nx][ny]=1;
                        }
                    }
                }
            }
            for (int ii=1;ii<=n;ii++)
                for (int jj=1;jj<=m;jj++) if (dis[ii][jj]<=T) ans=max(ans,(ii-i)*(ii-i)+(jj-j)*(jj-j));
        }
    ans=sqrt(ans);
    printf("%.6f\n",ans);
    return 0;
}