Fibonacci using boost::multiprecision::cpp_int

boost_mp_cppint_fib.cpp

#include <boost/multiprecision/cpp_int.hpp>
#include <iostream>

int main() {
    boost::multiprecision::cpp_int n1 = 0, n2 = 1;
    for (long i = 1; i <= 1000000; ++i) {
        n1 = std::exchange(n2, n1 + n2);
    }
    std::cout << n2;
}