#include <functional>

int accumulate(std::vector<int>::iterator begin,
               std::vector<int>::iterator end,
               int initial,
               std::function<int(int, int)> func)
{
    int result = initial;

    for (std::vector<int>::iterator it = begin; it != end; ++it)
    {
        result = func(result, *it);
    }

    return result;
}