Need a bit help with std::map and / or multimaps and algorithm

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Hello.

Im stuck with some problem(s).
Currently i have a std::map like this:

map<int, int> mymap;

In my procedure i add some items to this. When i have no duplicates for keys, all seems to work.
Few examples of my keys and values (just examples) just to get the idea:
Without duplicate keys:

mymap[257]=10;
mymap[94]=25;
mymap[98]=55;
mymap[21]=11;

When i need to work with duplicates (when one key can be used more than 1 time but different value)

mymap[257]=10;
mymap[94]=25;
mymap[98]=55;
mymap[98]=70;
mymap[21]=11;

I know that for duplicate keys with different values i should use multimap.

Lets say i switch to multimap..

Now if you look the duplicates example above, you see that when i need to get value of 98 i get it with:

int i = mymap[98];
// i is now: 55

Whats even more important, sometimes i need the latest value of the specific key

In this case:

int i = mymap[98];
// i MUST be 70

Is there any function for multimap or algorithm that returns me the latest specific "KEY" from multimap ?
Or there some other containers that could help me?

If its possible i would like to avoid multimap completely. I have seen that it differs from map pretty a lot and causes troubles in many areas.

What about pairs?
I can use C++11, boost and other latest technology if that matters.

TIA for any tip or help.