https://pintia.cn/problem-sets/994805342720868352/problems/994805350803292160
#include<bits/stdc++.h>
using namespace std;
const int N=1e3+10;
int n,k,st;
string s[N];
map<string,int>mp;
int main(void)
{
cin>>n>>k>>st;
for(int i=1;i<=n;i++) cin>>s[i];
bool flag=0;
for(int i=st;i<=n;i+=k)
{
if(!mp[s[i]]) cout<<s[i]<<endl,mp[s[i]]++,flag=1;
else
{
while(i<=n&&mp[s[i]]) i++;
if(i<=n) cout<<s[i]<<endl,mp[s[i]]++,flag=1;
}
}
if(!flag) puts("Keep going...");
return 0;
}