#include<bits/stdc++.h> using namespace std; int l,n,m,d[50005],lef,rig,mid,ans; bool f(int x){ int i=0,next=0,cnt=0; while(next<=n){ next++; if(d[next]-d[i]<x)i=next; else cnt++; } return (cnt<=m); } int main(){ cin>>l>>n>>m; for(int i=1;i<=n;i++){ cin>>d[i]; } d[n+1]=l; lef=1;rig=l;mid=(l+1)/2; while(lef<=rig){ if(f(mid)){ ans=mid; l=mid+1; } else rig=mid-1; mid=(lef+rig)/2; } cout<<ans; return 0; }