#include<iostream>

#include<forward_list>

#include<string>

using namespace std;

void insert(forward_list<string> &flist,string s1,string s2)

{

    auto prev=flist.before_begin();

    auto curr=flist.begin();

    while(curr!=flist.end())

    {

        if(*curr==s1)

        {

            flist.insert_after(curr,s2);

            break;

        }

        else

        {

            prev=curr;

            ++curr;

        }

    }

    if(curr==flist.end())

        flist.insert_after(prev,s2);

}

int main()

{

    forward_list<string> flist={"a","b","c","d","e"};

    insert(flist,"f","b");

    for(auto f:flist)

        cout<<f<<" ";

    cout<<endl;

    return ;

}