projecteuler---->problem=10----Summation of primes

title:

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

Find the sum of all the primes below two million.

import math,time
def isOk(a):
	for i in range(2,int(math.sqrt(a))+1):
		if a%i==0:
			return False
	return True
s=0
begin=time.time()
for i in range(2,2000000):
	if isOk(i):
		s += i	
print s
end = time.time()
print end-begin