#include <bits/stdc++.h>
using namespace std;
long long L,n,m,q,a[10000005]; 
long long JS(int x){
	int count=0,last=0;
    for(int i=1;i<=n;i++)
        if(a[i]-last<x)count++;
        	else last=a[i];
    if(count>m)return 0;
return 1;
} 
signed main(){
    ios::sync_with_stdio(0); 
	cin>>L>>n>>m; 
    for(int i=1;i<=n;i++)cin>>a[i]; 
    a[n+1]=L; 
	int l=0,r=L; 
	while(l<=r){ 
    	long long mid=(l+r)/2;
    	if(JS(mid))l=mid+1,q=mid; 
    	else r=mid-1; 
	}
    cout<<q;
	return 0;
}