# Calculate the sum of all multiples of 3, and all multiples of 5, but not multiples of both, up to 1000.

lim = 1000

fstMult = 0
fstInc = 3

sndMult = 0
sndInc = 5

bothMult = 0
bothInc = 15

sum = 0

while ( fstMult < (lim - fstInc) )
    fstMult = fstMult + fstInc
    sum = sum + fstMult
end

while ( sndMult < (lim - sndInc) )
    sndMult = sndMult + sndInc
    sum = sum + sndMult
end

while ( bothMult < (lim - bothInc) )
    bothMult = bothMult + bothInc
    sum = sum - bothMult
end

puts sum