#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5,INF=0x3f3f3f3f;
typedef long long LL;
int L,n,k,ans,a[N],l,r;
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 = L,a[++n] = L;
    while(l<=r){
        int mid=l+r>>1;
        if(check(mid))ans = mid,r = mid-1;
        else l = mid+1;
    }
    cout<<ans;
    return 0;
}