Convention

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

int n, m, c;
vector<ll> wtime;
ll l, r;
ll ans;

bool check(int mid){
    ll cur = wtime[0];
    //int ccw = 1;
    int cib = 1;
    int res = 1;
    //cout << "mid: " << mid << '\n';
    for(int i=1; i<n; i++){
        //cout << "wtime[i]: " << wtime[i] << '\n';
        if(cib>=c || wtime[i]-cur>mid){
            cib = 1;
            cur = wtime[i];
            //ccw++;
            res++;
        }else{
            cib++;
        }
    }
    return res<=m;
}

int main(){
    freopen("convention.in", "r", stdin);
    freopen("convention.out", "w", stdout);

    cin >> n >> m >> c;
    wtime.resize(n);
    for(int i=0; i<n; i++){
        cin >> wtime[i];
        r = max(r, wtime[i]);
    }
    sort(wtime.begin(), wtime.end());
    ll omid = 0;
    while(l<r){
        ll mid = (l+r)/2;
        if(omid == mid) break;
        if(check(mid)){
            r = mid;
            ans = mid;
        }else{
            l = mid;
        }
        omid = mid;
    }
    cout << ans << '\n';

    return 0;
}