fibonacci.c

unsigned int fibonacci(unsigned int n) {
    if (n > 2) {
        unsigned int a = 1, b = 1;
        while (n-- > 2) {
            b = a + b;
            a = b - a;
        }
        return b;
    } else if (n) {
        return 1;
    } else {
        return 0;
    }
}