//============================================================================
// Name        : mmmmmmmm.cpp
// Author      : sameh mohamed
// Copyright   : don't try i'm warnning you......
// Description : Hello World
//============================================================================
//Egypt came then History
//Pharoas were coders but using different compilers{}{}{}{}{}}}}{{{{@#$%^^&&$$$###()()(***)))([][][][][]]][
#include<bits/stdc++.h>
#include <iostream>
#include<string>
#include<algorithm>
#include<set>
#include<vector>
#include<map>
#include<cmath>
using namespace std;
long long ss(long long n)
{
	long long c=0;
	while(n)
	{
		long long m=log2(n);
		n=n-exp2(m);
		c++;
	}
	return c;
}
long long gcd(long long a,long long b)
{
	if(a==0)
		return b;
	else if(b==0)
		return a;
	else
	while(a!=b)
	{
		if(a>b)
			a-=b;
		else
			b-=a;
	}
	return a;
}
long long minc=1e9;
int main()
{
int n,d;
cin>>n>>d;
long long a[n][2];
for(int i=0;i<n;i++)
{
	cin>>a[i][0]>>a[i][1];
	long long m=min(a[i][0],a[i][1]);
	minc=min(minc,m);

}
long long s=0;
for(int i=0;i<n;i++)
{
	long long h=min(a[i][0],a[i][1]);
	long long m=min(a[i][0]+a[i][1],h+d+minc);
	s+=m;
}
cout<<s;
return 0;
}