#include<iostream>

#include<cstring>

#include<cstdio>

#include<utility>

#include<queue>

#include<cmath>

using namespace std;

double get_dis(int x,int y,int a,int b){

    return sqrt(1.0*(x-a)*(x-a)+1.0*(y-b)*(y-b));

}

struct Node{

    int x,y,d;

    Node(int x,int y,int d):x(x),y(y),d(d){}

    Node(){}

    bool operator < (const Node& tmp) const{

        return d>tmp.d;

    }

};

const int maxn=;

int mp[maxn][maxn];

int n,m,t;

char str[maxn];

double ans;

int d[maxn][maxn],vis[maxn][maxn];

const int dx[]={-,,,};

const int dy[]={,,-,};

void bfs(int sx,int sy,int t){

    if(mp[sx][sy]==) t--;

    if(t<) return;

    memset(d,0x7f,sizeof(d));

    memset(vis,,sizeof(vis));

    priority_queue<Node> Q;

    Q.push(Node(sx,sy,)),d[sx][sy]=,vis[sx][sy]=;

    while(!Q.empty()){

        int x=Q.top().x,y=Q.top().y;

        ans=max(ans,get_dis(sx,sy,x,y));

        Q.pop();

        for(int i=;i<;i++){

            int a=x+dx[i],b=y+dy[i];

            if(a<||a>=n||b<||b>=m) continue;

            if(vis[a][b]||mp[a][b]+d[x][y]>t) continue;

            d[a][b]=d[x][y]+mp[a][b],vis[a][b]=,Q.push(Node(a,b,d[a][b]));

        }

    }

}

int main(){

    while(scanf("%d%d%d",&n,&m,&t)==){

        for(int i=;i<n;i++){

            scanf("%s",str);

            for(int j=;j<m;j++){

                mp[i][j]=str[j]-'';

            }

        }

        ans=-;

        for(int i=;i<n;i++){

            for(int j=;j<m;j++){

                bfs(i,j,t);

            }

        }

        printf("%.6lf\n",ans);

    }

    return ;

}