#include <bits/stdc++.h> using namespace std; long long n,m,a[2100000],l; bool hsg(int b){ int c=0,p=0; for(int i=1;i<=n;i++){ if(a[i]-p<b) c++; else p=a[i]; } return c<=m; } int main(){ scanf("%d%d",&l,&n,&m); for(int i=1;i<=n;i++){ scanf("%d%d",&a[i]); } int l2=1,r2=1,mid; while(l2<=r2){ mid=(l2+2)/2; if(hsg(mid)) l2=mid+1; else r2=mid-1; } cout<<l2-1; return 0; }