#include <stdio.h>
int l,n,m,a[50010]={0};
int main(){
	scanf("%d%d%d",&l,&n,&m);
	for(int i=1;i<=n;i++){
		scanf("%d",&a[i]);
	}	
	if(n==m){
		printf("%d",l);
		return 0;
	}
	int left=0,right=l;
	while(left<=right){	
		int temp=0,num=0;
		int mid=left+(right-left)/2;
		for(int i=1;i<=n;i++){
			if(a[i]-temp>=mid){
				temp=a[i];
			}
			else num++;
		}
		if(num>m)right=mid-1;
		else left=mid+1;
	}
	printf("%d",right);
	return 0;
}