#include

#include

#include

#include

#include

#include

using namespace std;

const int N = 5e4 +10;

const int INF=0x3f3f3f;

int n,mid,m,a[N],l,r,ans,L;

bool check(int k){

int last = 0;

int sum = 0;

for(int i = 1;i<=n;i++){

if(a[i] - last < k)

sum++;

else

last = a[i];

}

return sum <= m;

}

int main(){

cin>>L>>n>>m;

for(int i = 1;i<=n;i++)

cin>>a[i];

a[++n] = L;

r = L;

while(l<=r){

int mid = l + r >>1;

if(check(mid)){

ans = mid;

l = mid + 1;

}

else

r = mid - 1;

}

cout<<ans;

}