#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,L; cin >> N >> L;
    int K; cin >> K;
    vector<int> A(N);
    for(auto &a : A) cin >> a;
    A.insert(A.begin(),0);
    A.push_back(L);
    N++;

    int low = 0,high = 1001001001;
    while(high-low > 1){
        int mid = (high+low)/2;
        vector<int> To(N,-1),C(N,N+1);
        int pos = 0;
        for(int i=0; i<N; i++){
            while(pos <= N && A.at(i)+mid > A.at(pos)) pos++; 
            if(pos > N) break;
            To.at(i) = pos;
            C.at(i) = pos-i;
        }
        for(int i=N-2; i>=0; i--) C.at(i) = min(C.at(i),C.at(i+1));
        bool ok = false;
        for(int i=0; i<N; i++){
            int to = To.at(i);
            if(to == -1 || to == N) continue;
            int use = to-i+C.at(to);
            if(use+K-1 <= N){ok = true; break;}
        }
        if(ok) low = mid;
        else high = mid;
    }
    cout << low << endl;
}