#include <bits/stdc++.h>
using namespace std;
bool check(vector<int>& nums,long mid,int m){
    int cnt=0;
    long sum=0;
    for(int i=0;i<=nums.size();i++){
        sum = nums[i];
        while(sum<mid && i<nums.size()){
            i++;
            sum+=nums[i];
            cnt++;
        }
    }
    if(cnt<=m){
        return true;
    }else{
        return false;
    }
}
int main(){
    int l,n,m;
    cin>>l>>n>>m;
    vector<int> nums(n);
    int now,before=0;
    for(int i=0;i<n;i++){
        cin>>now;
        nums.push_back(now-before);
        before = now;
    }
    nums.push_back(l-before);
    long x,y;
    x=0,y=l;
    long mid,ans;
    while(x<=y){
        mid=(x+y)/2;
        if(check(nums,mid,m)){
            ans=mid;
            x=mid+1;
        }else{
            y=mid-1;
        }
    }
    cout<<ans<<endl;
    return 0;
}