#include<bits/stdc++.h>
using namespace std;
const int N = 1e6 +10;
const int INF=0x3f3f3f;
int ans,l,r,L,n,k,a[N];
bool check(int mid){
    int sum = 0;
    for(int i = 2;i<=n;i++)
    sum+=(a[i] - a[i-1] - 1) / mid;
    return sum <= k;
}
int main(){
    cin>>L>>n>>k;
    for(int i = 1;i<=n;i++)
    cin>>a[i];
    sort(a+1,a+n+1);
    r = a[n] - 1;
    while(l<=r){
        int mid = l + r >>1;
        if(check(mid)){
            ans = mid;
            r = mid - 1;
        }
            else
                l = mid + 1;
      }
    cout<<ans;
}