This?

#include <bits/stdc++.h>
using namespace std;
unordered_map<string,int> S;
int main(void){
    string s;
    int N;
    cin>>N;
    for(int i(0);i<N;++i){
        cin>>s;
        if(S.count(s))cout<<s<<++S[s]<<endl;
        else S[s]=0,cout<<"OK\n";
    }
    return 0;
}