var v:array[1..100] of byte;
n,i,j,s:integer;

begin

read(n);

for i:=1 to n do
read(v[i]);

s:=0;

for i:=1 to n-1 do

begin
If (v[i]=v[i+1]) and (v[i]=1) then begin v[i+1]:=(v[i]+1)mod 2; inc(s);  end;
end;


write(s);

readln;
readln;
end.