#include<bits/stdc++.h>
using namespace std;
int main()
{
	freopen("waterj.in","r",stdin);
	freopen("waterj.out","w",stdout);
	int i,n,m,c,c2,tim=0,first,w[10010],nexw[10010],befw[10010];
	cin>>n>>m;
	for (i=1;i<=n;i++)
	{
		cin>>w[i];
		nexw[i]=i+1;
		befw[i]=i-1;
	}
	first=1;
	c=n;
	while (c)
	{
		tim++;
		c2=m;
		for (i=first;c>0&&c2>0&&i<=n;i=nexw[i])
		{
			c2--;
			w[i]--;
			if (w[i]==0)
			{
				c--;
				if (befw[i]==0)
					first=nexw[i];
				nexw[befw[i]]=nexw[i];
				befw[nexw[i]]=befw[i];
			}
		}
	}
	cout<<tim<<endl;
	return(0);
}