#include<bits/stdc++.h>
using namespace std;
int n,c,gl,mp[5005];long long ans=9999999;
struct node{
	int g;
	bool k;
}deng[1000005];
void dfs(bool dt,int w,long long hao){
	long long z,n=0;
	while(!deng[w].k){w=w+dt*2-1;
	if(w&&w<=mp[n])return;
		for(int i=1;i<=n;i++) z+=deng[mp[i]].g*deng[mp[i]].k;		
	}deng[w].k=0;
	dfs(1,w+1,hao+z);
	dfs(0,w-1,hao+z);
	for(int i=1;i<=n;i++)n+=deng[mp[i]].k;
	if(!n)ans=min(ans,hao+z);
}
int main(){
	cin>>n>>c;
	for(int i=1;i<=n;i++){
		scanf("%d%d",&mp[i],&gl);
		deng[mp[i]].k=1,deng[mp[i]].g=gl;
	}
	dfs(1,c,0);
	cout<<ans;
}