#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/tail.hpp>
 
int func(const std::vector<int>& v)
{
    using namespace boost::accumulators;
    accumulator_set<int, features<tag::tail<right> > > acc(tag::tail<right>::cache_size = 3);
    acc = for_each(v.begin(), v.end(), acc);
    return accumulate(tail(acc).begin(), tail(acc).end(), 0);
}
int main()
{
    int data[] = {1,2,3,4,5,6,7,8,9,10,20,30};
    std::vector<int> v(data, data+sizeof data/sizeof *data);
    std::cout << func(v) << '\n';
}
 

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