#include <bits/stdc++.h>
#define F first
#define S second
#define int long long
using namespace std;
const int N = 3e2 + 2 , inf = 1e18;
int n , h , a[N] , c[N] , prfmn[N] , dp[N][N][N][2] , nex[N];
int f(int k , int j)
{
int tmp = k / j;
int res = tmp * k - tmp * (tmp + 1) * j / 2;
res *= h;
return res;
}
signed main()
{
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0); cout.tie(0);
cin >> n >> h;
vector <pair<int ,int>> vec;
for(int i = 1 ; i <= n ; i++)
{
int x , y; cin >> x >> y;
vec.push_back(make_pair(x , y));
}
sort(vec.begin() , vec.end());
for(int i = 0 ; i < n ; i++)
{
a[i] = vec[i].F;
c[i] = vec[i].S;
prfmn[i] = c[i];
}
nex[n - 1] = n;
a[n] = inf;
for(int i = n - 2 ; i >= 0 ; i--)
nex[i] = (a[i] == a[i + 1] ? nex[i + 1] : i + 1);
/*for(int i = 0 ; i < n ; i++)
cout << i << " : " << nex[i] << endl;
for(int i = 0 ; i < n ; i++)
cout << a[i] << " ";
cout << '\n';
for(int i = 0 ; i < n ; i++)
cout << c[i] << " ";
cout << '\n';*/
for(int i = 1 ; i < n ; i++)
prfmn[i] = min(prfmn[i] , prfmn[i - 1]);
for(int i = n ; i >= 1 ; i--) for(int j = 0 ; j <= n ; j++)
{
if(i >= j)
continue;
dp[n][i][j][0] = dp[n][i + 1][j][0] + prfmn[n - 1];
dp[n][i][j][0] = min(dp[n][i][j][0] , f(j , i));
dp[n][i][j][1] = dp[n][i][j][0];
}
for(int i = n - 1 ; i >= 1 ; i--) for(int j = n ; j >= 1 ; j--) for(int k = 0 ; k <= i ; k++)
{
int tmp = nex[i] - i + k;
if(tmp <= j)
{
dp[i][j][k][0] = dp[nex[i]][j][0][0];
}
else
{
if(a[i] + 1 == a[nex[i]])
dp[i][j][k][0] = dp[nex[i]][j][tmp - j][0] + (tmp - j) * h;
else
dp[i][j][k][0] = dp[nex[i]][j][tmp - j][1] + (tmp - j) * h;
dp[i][j][k][0] = min(dp[i][j][k][0] , dp[i][j + 1][k][0] + prfmn[i - 1]);
}
if(k <= j)
{
dp[i][j][k][1] = dp[i][j][0][0];
}
else
{
tmp = (a[i] - a[i - 1] - 1) * j;
if(tmp >= k)
dp[i][j][k][1] = dp[i][j][0][0] + f(k , j);
else
{
dp[i][j][k][1] = dp[i][j][k - tmp][0] + f(tmp , j) + (k - tmp) * (a[i] - a[i - 1] - 1) * h;
}
dp[i][j][k][1] = min(dp[i][j][k][1] , dp[i][j + 1][k][1] + prfmn[i - 1]);
}
//cout << i << " " << j << " " << k << " " << dp[i][j][k][0] << " " << dp[i][j][k][1] << endl;
}
if(a[0] + 1 == a[nex[0]])
cout << dp[nex[0]][1][nex[0] - 1][0] + (nex[0] - 1) * h << '\n';
else
cout << dp[nex[0]][1][nex[0] - 1][1] + (nex[0] - 1) * h << '\n';
return 0;
}
