#include<bits/stdc++.h> using namespace std; int l,n,m,a[50086],l2,r2,mid; bool d(int x){ int cnt=0; int p=0; for(int i=1;i<=n;i++){ if(a[i]-p<x) cnt++; else p=a[i]; } return cnt<=m; } int main(){ scanf("%d%d%d",&l,&n,&m); for(int i=1;i<=n;i++){ scanf("%d",&a[i]); } l2=1,r2=l; while(l2<=r2){ mid=l2+r2>>1; if(d(mid)) l2=mid+1; else r2=mid-1; } printf("%d",l2-1); return 0; }