[SCOI2007] 修车

program repair;
type ptype=^node;
     node=record
          v,w,flow,cost:longint;
          next,op:ptype;
          end;
const maxn=10000;
var head,prep:array[0..maxn] of ptype;
    visit:array[0..maxn] of boolean;
    q,dis,pre:array[0..maxn] of longint;
    time:array[0..100,0..100] of longint;
    n,m,i,j,k,st,ed:longint;
function min(a,b:longint):longint;
begin
  if a<b then exit(a) else exit(b);
end;

procedure insert(u,v,w1,w2,cost:longint);
var p1,p2,q:ptype;
begin
  new(p1);
  p1^.v:=v;p1^.w:=w1;p1^.flow:=0;p1^.cost:=cost;p1^.next:=nil;
  q:=head[u];
  if q=nil then head[u]:=p1 else
    begin
      q:=head[u];
      head[u]:=p1;
      p1^.next:=q;
    end;
  new(p2);
  p2^.v:=u;p2^.w:=w2;p2^.flow:=0;p2^.cost:=-cost;p2^.next:=nil;
  q:=head[v];
  if q=nil then head[v]:=p2 else
    begin
      q:=head[v];
      head[v]:=p2;
      p2^.next:=q;
    end;
  p1^.op:=p2;p2^.op:=p1;
end;

function spfa:boolean;
var star,rear,x:longint;
    y:ptype;
begin
  fillchar(q,sizeof(q),0);
  fillchar(pre,sizeof(pre),0);
  fillchar(visit,sizeof(visit),false);
  fillchar(dis,sizeof(dis),$7f);
  star:=1;rear:=1;q[star]:=st;visit[st]:=true;dis[st]:=0;
  while star<=rear do
    begin
      x:=q[star];
      y:=head[x];
      while y<>nil do
        begin
          if (dis[y^.v]>dis[x]+y^.cost) and (y^.w>y^.flow) then
            begin
              dis[y^.v]:=dis[x]+y^.cost;
              pre[y^.v]:=x;
              prep[y^.v]:=y;
              if not visit[y^.v] then
                begin
                  inc(rear);
                  q[rear]:=y^.v;
                  visit[y^.v]:=true;
                end;
            end;
          y:=y^.next;
        end;
      visit[x]:=false;
      inc(star);
    end;
  spfa:=not (dis[ed]=2139062143);
end;

function addcost:longint;
var x,addflow:longint;
    y:ptype;
begin
  x:=ed;
  addflow:=maxlongint;
  while x<>st do
    begin
      y:=prep[x];
      addflow:=min(addflow,y^.w-y^.flow);
      x:=pre[x];
    end;
  x:=ed;
  while x<>st do
    begin
      y:=prep[x];
      inc(y^.flow,addflow);
      dec(y^.op^.flow,addflow);
      x:=pre[x];
    end;
  addcost:=addflow*dis[ed];
end;

function mincost:longint;
begin
  mincost:=0;
  while spfa do inc(mincost,addcost);
end;

begin
  //assign(input,‘repair.in‘);reset(input);
  //assign(output,‘repair.out‘);rewrite(output);
  readln(m,n);
  st:=0;ed:=n+n*m+1;
  for i:=1 to n do
    for j:=1 to m do
      read(time[i,j]);
  for i:=1 to n do
    insert(st,i,1,0,0);
  for i:=n+n*m downto n+1 do
    insert(i,ed,1,0,0);
  for i:=1 to n do
    for j:=1 to m do
      for k:=1 to n do
        insert(i,j*n+k,1,0,(n-k+1)*time[i,j]);
  writeln(mincost/n:0:2);
  //close(input);close(output);
end.