#include <numeric>
#include <span>
#include <stdexcept>

double average(std::span<const double> values) {
    if (values.empty()) {
        throw std::invalid_argument("values must not be empty");
    }
    const double sum = std::accumulate(values.begin(), values.end(), 0.0);
    return sum / static_cast<double>(values.size());
}