#include<stdio.h>

#include<string.h>

#define inf 0x7fffffff

#define min(a,b) (a<b?a:b)

#define S 0

#define T 1001

#define length 2005

struct zxy{int to,next,c,v;}edge[];

int n,m,cnt=,head[],dist[],que[],pre[];

bool vis[];

inline int in(){

    int x=,f=;char ch=getchar();

    while(ch<''||ch>'') f=ch=='-'?-:,ch=getchar();

    while(ch>=''&&ch<='') x=x*+ch-'',ch=getchar();

    return x*f;

}

inline void ins(int x,int y,int v,int l){

    edge[++cnt].to=y,edge[cnt].next=head[x],edge[cnt].v=v,edge[cnt].c=l,head[x]=cnt;

    edge[++cnt].to=x,edge[cnt].next=head[y],edge[cnt].v=,edge[cnt].c=l*(-),head[y]=cnt;

}

bool SPFA_costflow(int s,int e){

    memset(dist,/,sizeof(dist));

    register int h=,t=,w,v;

    que[]=s; vis[s]=; dist[s]=;

    while(h!=t){

        (++h)%=length;

        w=que[h];

        for (register int i=head[w]; i; i=edge[i].next)

            if (dist[edge[i].to]>dist[w]+edge[i].c&&edge[i].v){

                v=edge[i].to; pre[v]=i;

                dist[v]=dist[w]+edge[i].c;

                if (!vis[v]){

                    vis[v]=;

                    if (dist[v]<dist[h+]){

                        que[h]=v;

                        h=(h-+length)%length;

                    }

                    else{

                        (++t)%=length;

                        que[t]=v;

                    }

                }

            }

        vis[w]=;

    }

    return dist[e]!=dist[T+];

}

int cost_flow(int s,int t){

    int cost=;

    while(SPFA_costflow(s,t)){

        int mi=inf;

        for (register int i=t; i; i=edge[pre[i]^].to)

            mi=min(mi,edge[pre[i]].v);

        for (register int i=t; i; i=edge[pre[i]^].to)

            edge[pre[i]].v-=mi,edge[pre[i]^].v+=mi;

        cost+=dist[t]*mi;

    }

    return cost;

}

void init(){

    m=in(),n=in();

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

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

            int l=in();

            for (int k=; k<=n; ++k)

                ins(i,j*n+k,,k*l);

            ins(j*n+i,T,,);

        }

        ins(S,i,,);

    }

}

int main(){

    init();

    printf("%.2lf",1.0*cost_flow(S,T)/n);

}