#include<cstdio>
typedef long long ll;

ll get_interest(ll balance, int r)
{
	ll interest = balance / (ll)r;
	if (balance % (ll)r != 0)
	{
		++interest;
	}
	return interest;
}

bool can(const int *arr, int n, int r, ll balance, ll sum)
{
	for (int i = 0; i < n; ++i)
	{
		balance += get_interest(balance, r);
		balance -= (ll)arr[i];
		
		sum -= (ll)arr[i];
		
		if (balance <= 0)
		{
			return true;
		}
		if (balance > sum)
		{
			return false;
		}
	}
	return false;
}

int main()
{
	int n, r;
	static int arr[200005];
	ll x = 0, y = 0;
	ll sum = 0;
	ll ans = 0;
	
	scanf("%d%d", &n, &r);
	
	for (int i = 0; i < n; ++i)
	{
		scanf("%d", &arr[i]);
		sum += (ll)arr[i];
	}
	
	y = sum;
	
	while (x <= y)
	{
		ll mid = x + (y - x) / 2ll;
		
		if (can(arr, n, r, mid, sum))
		{
			x = mid + 1;
			ans = mid;
		}
		else
		{
			y = mid - 1;
		}
	}
	
	printf("%lld\n", ans);
	return 0;
}