Untitled

#include <stdio.h>
#define LIM 4000000

int main()
{
    /*
        a = 1, b = 2, c = 3. -> a = 2, b = 3, c = 5. -> a = 3, b = 5, c = 8.
        Basically we move forward with a single element each time, until the limit
        is reached, and simply check if b (starting from the first even number) is even.
    */
    
    int a = 1, b = 2, c = 0, sum = 0, temp;
    while (b < LIM)
    {
        if (b % 2 == 0)
            sum += b;
        c = a + b;
        a = b;
        b = c;
    }
    printf("%d", sum);
    return 0;
}