include<bits/stdc++.h>

using namespace std; int len,n,k,l,r,mid; int a[100010]; bool check(int mid){

int c=0;
for(int i=2;i<=n;i++){
	if(a[i]-a[i-1]>=mid){
		c+=(a[i]-a[i-1])/mid;
		if((a[i]-a[i-1])%mid==0){
			c--;
		}
	}
}
if(c>k) return 0;
return 1;

} int main(){

cin>>l>>n>>k;
for(int i=1;i<=n;i++){
	cin>>a[i];
}
sort(a+1,a+n+1);
l=0,r=l;
while(l<=r){
	mid=l+r>>1;
	if(check(mid))
		r=mid-1;
	else
		l=mid+1;
}
cout<<l;
return 0;

}