I am unable to delete one of the key from map successfully in c++

I have a map in the following format -

map<int, vector<int>> myGraph;

I am trying to delete a key from myGraph using -

myGraph.erase(firstValue);

Here firstValue is key from myGraph.

The value of corresponding to firstValue key is getting deleted but the key still exists in the map.

int main(void) {
    string name;
    map<int, vector<int>> myGraph;
    int temp, value;
    while(getline(cin, name)) {
        stringstream stream(name);
        stream >> value;
        while(stream >> temp) {
            myGraph[value].push_back(temp);
        }
    }
        while(myGraph.size() > 2) {
            auto iter = myGraph.begin();
            advance(iter, rand() % myGraph.size());
            auto mik = iter->second.begin();
            cout << iter->second.size() << " " << iter->first<< endl;
            advance(mik, rand() % iter->second.size());
            int firstValue = iter->first, secondValue = *mik;
            myGraph[secondValue].insert(myGraph[secondValue].end(), iter->second.begin(), iter->second.end());
            myGraph.erase(firstValue);
            myGraph[secondValue].erase(remove(myGraph[secondValue].begin(), myGraph[secondValue].end(), firstValue), myGraph[secondValue].end());
            for(auto iterate = myGraph.begin(); iterate != myGraph.end(); iterate++) {
                replace(iterate->second.begin(), iterate->second.end(), firstValue, secondValue);
            }
        }

    cout << myGraph.size() << endl;
    return 0;
}