#include<iostream>

#include<stack>

#include<queue>

#include<cstring>

#include<cmath>

#include<algorithm>

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;

}