#include<stdio.h>

 #include<string.h>

 #include<stdlib.h>

 #include<algorithm>

 #include<queue>

 //#include<iostream>

 using namespace std;

 int n,R,C,v;

 #define maxn 10011

 #define maxm 80011

 int a[][];double pw[];

 struct Graph

 {

     struct Edge{int to,next;double v;}edge[maxm];int first[maxn],le;

     Graph() {memset(first,,sizeof(first));le=;}

     void in(int x,int y,double v) {Edge &e=edge[le];e.to=y;e.v=v;e.next=first[x];first[x]=le++;}

     double dis[maxn];bool vis[maxn];

     struct qnode

     {

         int id;double v;

         bool operator > (const qnode &b) const {return v>b.v;}

     };

     priority_queue<qnode,vector<qnode>,greater<qnode> > q;

     double dijkstra(int s,int t)

     {

         memset(vis,,sizeof(vis));

         for (int i=;i<=n;i++) dis[i]=1e15;dis[s]=;

         q.push((qnode){s,});

         while (!q.empty())

         {

             const int now=q.top().id;const double d=q.top().v;q.pop();

             if (vis[now]) continue;

             vis[now]=;

             for (int i=first[now];i;i=edge[i].next)

             {

                 const Edge &e=edge[i];

                 if (dis[e.to]>d+e.v)

                 {

                     dis[e.to]=d+e.v;

                     q.push((qnode){e.to,dis[e.to]});

                 }

             }

         }

         return dis[t];

     }

 }g;

 int main()

 {

     pw[]=1.0;

     for (int i=;i<=;i++) pw[i]=pw[i-]*;

     for (int i=-;i>=-;i--) pw[i]=pw[i+]/;

     scanf("%d%d%d",&v,&R,&C);

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

         for (int j=;j<=C;j++)

             scanf("%d",&a[i][j]);

     n=R*C;

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

         for (int j=;j<=C;j++)

         {

             double now=1.0/(pw[a[][]-a[i][j]]*v);

             int id=(i-)*C+j;

             if (j>) g.in(id,id-,now);

             if (j<C) g.in(id,id+,now);

             if (i>) g.in(id,id-C,now);

             if (i<R) g.in(id,id+C,now);

         }

     printf("%.2f\n",g.dijkstra(,n));

     return ;

 }