#include <iostream>
#include <unordered_map>
#include <vector>
 
using namespace std;
 
int main() {
    int n;
    cin >> n;
 
    vector<int> arr(n);
    for(int i = 0; i < n; i++) {
        cin >> arr[i];
    }
 
    int k;
    cin >> k;
 
    vector<pair<int, int>> ans;
 
    unordered_map<int, int> mp;
 
    for(int i = 0; i < n; i++) {
        int currentElement = arr[i];
 
        if(mp.find(currentElement) != mp.end()) {
            int lastIndex = mp[currentElement];
            int distance = i - lastIndex; 
 
            if(distance <= k) {
                ans.push_back({lastIndex, i});
            }
        }
 
        mp[currentElement] = i;
    }
 
    for(const auto &p : ans) {
        cout << p.first << " : " << p.second << endl;
    }
 
    return 0;
}

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