The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.

My solution in Ruby:

```
def is_prime ( p )
if p == 2
return true
elsif p <= 1 || p % 2 == 0
return false
else
(3 .. Math.sqrt(p)).step(2) do |i|
if p % i == 0
return false
end
end
return true
end
end
sum = 0
for i in 2..2000000
if is_prime(i)
sum += i
end
end
puts sum
```