I solving the problems at Project Euler

I'm at problem 2

and I have made this program so far

but I dont know why it takes too much time to give me the answer

even if the fibonacci number is 4

the code is this

any hint on how to improve would be really appreciatedCode:#include <iostream> using namespace std; int main () { typedef unsigned long ul; ul n1 = 0; ul n2 = 1; ul n3; ul index1 = 0; long double sum = 0; while (index1 < 4) { n3 = n1 + n2; if ( n3 % 2 == 0 ) { sum += n3; } n1 = n2; n2 = n3; } cout << sum; return EXIT_SUCCESS; }

thanks