#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <numeric>
 
template<class T>
struct multiply_range : public std::binary_function<T, T, T> {
public:
    multiply_range() : i(0), j(1) { }
    T operator()(T a, T b) {
        if (!(this->i++ % 2) && (this->j++ % 2)) {
        return a * b;
            }
    }
private:
    std::size_t i, j;
};
 
 
int main() {
    std::vector<int> vec_numsx = {1,2,3,4,5};
    std::vector<int> vec_numsy = {5,6,7,8,9,10};
    std::cout << std::inner_product(vec_numsx.begin(), 
                                vec_numsx.end(), 
                                std::next(vec_numsy.begin()), 
                                0, 
                                std::plus<int>(),
                    multiply_range<int>());
    return 0;
}

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