#include <iostream>
#include <chrono>
#include <ctime>
 
int fibonacci(int n)
{
    if (n < 3) return 1;
    return fibonacci(n-1) + fibonacci(n-2);
}
 
int main()
{
    std::chrono::time_point<std::chrono::system_clock> start, end;
    start = std::chrono::system_clock::now();
    int result = fibonacci(42);
    end = std::chrono::system_clock::now();
 
    int elapsed_seconds = std::chrono::duration_cast<std::chrono::nanoseconds>
                             (end-start).count();
    std::time_t end_time = std::chrono::system_clock::to_time_t(end);
 
    std::cout << "finished computation at " << std::ctime(&end_time)
              << "elapsed time: " << elapsed_seconds << "ns\n";
}

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