已知公路总长L米,一共有K个赛道,你的赛车总是和公路上其他的普通的车走相反的方向,并且所有的车每秒沿赛道行驶1m
问题是:跑到终点最少撞多少次车?

 

program rq94;
var f:array[-10..100,-10..100]of longint;
    a:array[0..100,0..100]of longint;
    ans,m,n:longint;
procedure init;
  var i,j:longint;c:char;
  begin
    assign(input,'input.txt');reset(input);
    readln(m,n);
    for i:=m downto 1 do
      begin
        for j:=1 to n do
          begin
            read(c);
            if c='0' then a[i,j]:=0 else a[i,j]:=1;
          end;
        readln;
      end;
  end;
function min(a,b:longint):longint;
  begin
    if a>b then exit(b) else exit(a);
  end;
procedure work;
  var i,j,k:longint;
  begin
    for i:=1 to m do
      for j:=1 to n do
        begin
          f[i,j]:=maxlongint;
          f[i,j]:=min(f[i,j],f[i-2,j]+a[i-1,j]);
          if j>1 then f[i,j]:=min(f[i,j],f[i-2,j-1]);
          if j+1<=n then f[i,j]:=min(f[i,j],f[i-2,j+1]);
          f[i,j]:=f[i,j]+a[i,j];
        end;
    ans:=maxlongint;
    for i:=1 to n do
      ans:=min(ans,f[m,i]);
    writeln(ans);
  end;
begin
  init;
  work;
end.