Friday the 13th, Programmers Day C. Counting Fridays

• Time : $O(n)$
• Space : $O(1)$

With Gnat.IO; use Gnat.IO;
 
procedure Main is
    caso, sz : Integer;
    ln : String(1..10);
    c : Character;
    y, m, d, di, cnt: Integer;
    
begin
    get(caso);
    cnt:=0;
    for i in 1 .. caso loop
        get(y); get(c); get(m); get(c); get(d);
        di:= 1461 * (y + 4800 + (m - 14) / 12) / 4 +
        367 * (m - 2 - (m - 14) / 12 * 12) / 12 - 
        3 * ((y + 4900 + (m - 14) / 12) / 100) / 4 + 
        d - 32075;
        
        if d = 13 and (di mod 7) = 4 then
            cnt := cnt+1;
        end if;
        
    end loop;
    
    put(cnt);
    
end Main;