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MODULE Ch2;
IMPORT Out;
PROCEDURE IsPrime(N:INTEGER):BOOLEAN;
VAR I:INTEGER;
BEGIN
I := 5;
IF (N = 2) OR (N = 3) THEN RETURN TRUE END;
IF (N <= 1) OR (N MOD 2 = 0) OR (N MOD 3 = 0) THEN RETURN FALSE END;
WHILE I * I <= N DO
IF (N MOD I = 0) OR (N MOD (I+2) = 0) THEN RETURN FALSE END;
INC(I,6);
END;
RETURN TRUE;
END IsPrime;
PROCEDURE PrimeCount(N:INTEGER):INTEGER;
VAR I,Count:INTEGER;
BEGIN
Count := 0;
FOR I := 1 TO N-1 DO
IF IsPrime(I) THEN INC(Count) END;
END;
RETURN Count;
END PrimeCount;
BEGIN
Out.Int(PrimeCount(10),0); Out.Ln;
Out.Int(PrimeCount(15),0); Out.Ln;
Out.Int(PrimeCount(1),0); Out.Ln;
Out.Int(PrimeCount(25),0); Out.Ln;
END Ch2.
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