#include <iostream>

long long fibrTail(int n, long long a = 0, long long b = 1) {
    if (n == 0) return a;
    if (n == 1) return b;
    return fibrTail(n - 1, b, a + b);
}

int main() {
    int n = 50;
    std::cout << "Fibonacci of " << n << " using tail recursion is " << fibrTail(n) << std::endl;
    return 0;
}