#include <iostream>
#include <vector>
 
template <class fwdit> 
typename fwdit::value_type arithmetic_mean(fwdit begin, fwdit end) { 
 
    typedef typename fwdit::value_type res_type;
 
    res_type sum = res_type();
    size_t count = 0;
 
    for (fwdit pos = begin; pos!= end; ++pos) { 
        sum += *pos;
        ++count;
    }
    return sum/count;
}
 
int main() {
	std::vector< int> vi( 10, 3);
    vi[9] = 5;
    double average = arithmetic_mean( vi.begin(), vi.end());
    std::cout << average;
	return 0;
}

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