#include <bits/stdc++.h>
using namespace std;
int main(){
	int n,m,t,x,p;
	cin >> n >> m;
	int a[n],b[n];
	for (int i = 0;i < n;i ++)   cin >> a[i];
	for (int i = 0;i < m;i ++)   b[i] = a[i];
	t = m + 1;
	x = 1;
	while (x < 4){
		for (int i = 0;i < m;i ++)   b[i] -= 1;
		for (int i = 0;i < m;i ++){
			if (b[i] == 0 && t <= n){
				b[i] = a[t];
				t ++;
			} 
		}
		p = 0;
		for (int i = 0;i < m;i ++){
			if (b[i] == 0)   p ++;
		}
		if (p == 3){
			cout << x;
			break;
		}
		x ++;
	}
	cout << x;
    return 0;
}