#include <algorithm>
#include <string>
#include <map>
#include <iostream>

std::map<std::string, float> marks ={{"Joe", 90}, {"Jim", 85}};

float getAverageMark() 
{ 
	if ( marks.empty()) 
	    return 0; 
	return std::accumulate(marks.begin(), marks.end(), 0.0f, [&](float f, auto&pr) 
	{ return f + pr.second;}) / marks.size();
}

int main() 
{
	std::cout << getAverageMark();
}