#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
bool check(int mid, int n, int m, vector<int>& rocks) {
    int cur = 0;  
    int removed = 0; 
    for (int rock : rocks) {
        if (rock - cur < mid) {
            removed++;
        }
        else {
            cur = rock;
        }
    }
    return removed <= m;
}

int main() {
    int l, n, m;
    cin >> l >> n >> m;
    vector<int> rocks(n);
    for (int i = 0; i < n; i++) {
        cin >> rocks[i];
    }
    int left = 1, right = l;
    while (left < right) {
        int mid = (left + right + 1) / 2;
        if (check(mid, n, m, rocks)) {
            left = mid;
        }
        else {
            right = mid - 1;
        }
    }
    cout << left << endl;
    return 0;
}