MODULE AdditivePrimes EXPORTS Main;

IMPORT SIO,Fmt;

CONST
  Max = 500;

VAR
  Count:CARDINAL := 0;
  Prime:ARRAY[2..Max] OF BOOLEAN;

PROCEDURE DigitSum(N:CARDINAL):CARDINAL =
  BEGIN
    IF N < 10 THEN RETURN N
    ELSE RETURN (N MOD 10) + DigitSum(N DIV 10) END;
  END DigitSum;

PROCEDURE Sieve() =
  VAR J:CARDINAL;
  BEGIN
    FOR I := 2 TO Max DO Prime[I] := TRUE END;
    FOR I := 2 TO Max DIV 2 DO
      IF Prime[I] THEN
        J := I*2;
        WHILE J <= Max DO
          Prime[J] := FALSE;
          INC(J,I)
        END
      END
    END;
  END Sieve;

BEGIN
  Sieve();
  FOR N := 2 TO Max DO
    IF Prime[N] AND Prime[DigitSum(N)] THEN
      SIO.PutText(Fmt.F("%4s",Fmt.Int(N)));
      INC(Count);
      IF Count MOD 10 = 0 THEN SIO.Nl() END
    END
  END;
  SIO.PutText(Fmt.F("\nThere are %s additive primes less than %s.\n",
                    Fmt.Int(Count),Fmt.Int(Max)));
END AdditivePrimes.