#include<bits/stdc++.h>
using namespace std;

int n,m,s[10000];
int minn=999999;
int a;

int main()
{
	scanf("%d %d",&n,&m);
	for(int i=4;i<n+4;i++)
	{
		scanf("%d",&s[i]);
		if(i>6)
		{
			a=s[i]+s[i-1]+s[i-2];
			minn=min(a,minn);
		}
	}
	cout<<minn;
	return 0;
}