int one = 3;
int two = 4;
Hmm. one is not 3. two is not 4. Use variable names that make sense. These do not.
digitalRead(one);
digitalRead(two);
digitalRead(three);
What is the point of reading from a pin if you ignore the return value?
if (sum = 0){
= is an assignment operator. == is the equality operator. Back to the reference page for you.