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

#define int long long

const int N=305;

int a[N], cost[N], pos[N], sum[N], Min[N];
int dp1[N][N], dp2[N][N];
map <int,int> cnt, have, Mincost;

signed main()
{
	int n,m,K;
	cin >> n >> K;
	for(int i=1;i<=n;i++)
	{
		scanf("%lld %lld",&a[i],&cost[i]);
		cnt[a[i]]++;
		have[a[i]]++;
		if(have[a[i]]>1)
			Mincost[a[i]]=min(Mincost[a[i]],cost[i]);
		else
			Mincost[a[i]]=cost[i];

		int pos=a[i];
		while(cnt[pos]>=2)
		{
			cnt[pos]--;
			pos++;
			cnt[pos]++;
		}
	}

	int indx=0;
	for(auto x:cnt)
		pos[++indx]=x.first;
	n=indx;

	Min[0]=1e12;
	for(int i=1;i<=n;i++)
	{
		a[i]=have[pos[i]];
		if(a[i])
		{
			sum[i]=sum[i-1]+a[i];
			Min[i]=min(Min[i-1],Mincost[pos[i]]);
		}
		else
			sum[i]=sum[i-1], Min[i]=Min[i-1];
	}

	memset(dp2,0x3f,sizeof(dp2));
	dp2[0][1]=0;
	for(int i=1;i<=n;i++) //目前到第i层
	{
		memset(dp1,0x3f,sizeof(dp1));
		for(int cnt=a[i];cnt<=sum[i];cnt++)
			for(int Max=1;Max<=sum[i];Max++)
				dp1[cnt][Max]=dp2[cnt-a[i]][Max];

		memset(dp2,0x3f,sizeof(dp2));
		for(int cnt=0;cnt<=sum[i];cnt++)
			for(int Max=1;Max<=sum[i];Max++)
			{
				for(int j=0;j<=Max;j++)
				{
					if(cnt+j<=sum[i])
						dp2[cnt][Max]=min(dp2[cnt][Max],dp1[cnt+j][Max]);

					if(cnt+Max<=sum[i])
						dp2[cnt][Max]=min(dp2[cnt][Max],dp1[cnt+Max][j]+(Max-j)*Min[i-1]);
				}
				dp2[cnt][Max] += cnt*K;
			}
	}

	int ans=0x3f3f3f3f3f3f3f3f;
	for(int i=1;i<=n;i++)
		ans=min(ans,dp2[0][i]);
	printf("%lld\n",ans);
	return 0;
}