#include <iostream>
#include <map>
using namespace std;


int main()
{
    map<int,int> mymap={{1,0},{2,1},{9,2},{10,3},{11,4}};;
    for(auto it=mymap.rbegin();it!=mymap.rend();){
        int v=it->first;
        ++it;
        mymap.erase(v);
    }
    std::cout << "done";
}