求助！！

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<queue>
#include<vector>
#include<set>
using namespace std;
int l,n,k,a[1000010],ans;
bool check(int mid){
	int sum=0,last=1;
	for(int i=0;i<n;i++){
		if(sum>k) return 0;
		if(a[i]-last<=mid) last=a[i];
		else{
			sum++;
			last+=mid;
			i--;
		}
	}
	while(l-last>mid){
		if(sum>k) return 0;
		sum++;
		last+=mid;
	}
	return 1;
}
int main(){
	cin>>l>>n>>k;
	for(int i=0;i<n;i++) cin>>a[i];
	int low=0,high=l+1,mid;
	while(low<=high){
		mid=(low+high)/2;
		if(check(mid)){
			high=mid-1;
			ans=mid;
		}
		else low=mid+1;
	}
	cout<<ans;
	return 0;
}