int lucas(int x){

    int luca[50] = {2,1};
    int i;

    if (x == 0) return 2;
    if (x == 1) return 1;

    for(i=0;i<=x;i++){
        luca[i] = luca[i-1] + luca[i-2];
    }

    return luca[x];
}