type IFact {
    int fact(int n);
}

class FactRec() : IFact impl IFact {
    int fact(int n) {
        return factA(n, 1);
    }

    int factA(int n, int a) {
        if n == 0 { a; }
        else { factA(n - 1, a * n); };
    }

    export IFact : fact;
}

class FactAcc() : IFact impl IFact {
    int fact(int n) {
        int ret = 1;
        while (n > 1) {
          ret = ret * n;
          n   = n - 1;
        };
        return ret;
    }

    export IFact : fact;
}

int main(){
    (new FactRec:IFact()).fact(500) + (new FactAcc:IFact()).fact(500);
}