#include <map>
#include <iostream>

int main() {
    std::map<int, int> m{
            {1, 1}, {2, 1}, {3, 2}, {4, 1},
            {5, 2}, {6, 2}, {7, 1}, {8, 2}
    };

    // ▼▼▼ usuwanie ▼▼▼
    for (auto iter = m.begin(); iter != m.end();) {
        if (iter->second == 1) iter = m.erase(iter);
        else ++iter;
    }
    // ▲▲▲ usuwanie ▲▲▲

    for (auto [k, v] : m) {
        std::cout << k << ' ' << v << '\n';
    }
}