http://projecteuler.net/problem=2

#include <iostream>

using namespace std;

int main()
{
    int a = 1;
    int b = 2;
    int c = a + b;

    int nSum = 0;
    while (b <= 4000000)
    {
        if (b % 2 == 0)
        {
            nSum += b;
        }
        a = b;
        b = c;
        c = a + b;
    }

    cout << nSum << endl;
    return 0;
}