#include <iostream>
#include <algorithm>
using namespace std;
int L,M,N,a[50010];
bool aaa(int b)
{
    int cnt=0,pos=0;
    for (int i = 0; i < N; i++)
    {
        if (a[i-pos<b])cnt++;
        else pos=a[i];
    }
    if(L-pos<b)cnt++;
    return cnt <= M;
}
int main()
{
    cin >> L>> N>> M;
    for (int i = 0; i < N; i++)
    {
        cin >>a[i];
    }
    int l=1,r=L,ans=-1;
    while (l<r)
    {
        int mid = (l+r)>>1;
        if (aaa(mid)) l=mid+1,ans=mid;
        else r=mid-1;
    }
    cout << ans;
    return 0;
}