Problem 2

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

C++:

#include 
     
      using namespace std;const long N = 4000000;int main(){    long f1 = 1, f2 = 2, f3;    long ans = f2;    for(;;) {        f3 = f1 + f2;        if(f3 > N)            break;        if(f3 % 2 == 0) {            ans += f3;        }        f1 = f2;        f2 = f3;    }    cout << ans << endl;    return 0;}
     

Python:

ls=[1,1]ans=0while ls[-1] <4000000:	ls.append(ls[-1]+ls[-2])	if (ls[-1]&1) == 0:		ans+=ls[-1]print(ans)

Run results:

4613732