#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define rrep(i,n) for(int i=(int)(n)-1;i>=0;--i)
#define srep(i,s,t) for(int i=(int)(s);i<(int)(t);++i)
#define each(a,b) for(const auto& (a): (b))
#define all(v) (v).begin(),(v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)),v.erase(unique(all(v)),v.end())
#define cmx(x,y) x=max(x,y)
#define cmn(x,y) x=min(x,y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout<<#x<<" = "<<(x)<<endl
#define sar(a,n) {cout<<#a<<":";rep(pachico,n)cout<<" "<<a[pachico];cout<<endl;}

using namespace std;

template<typename S,typename T>auto&operator<<(ostream&o,pair<S,T>p){return o<<"{"<<p.fi<<","<<p.se<<"}";}
template<typename T>auto&operator<<(ostream&o,set<T>s){for(auto&e:s)o<<e<<" ";return o;}
template<typename S,typename T,typename U>
auto&operator<<(ostream&o,priority_queue<S,T,U>q){while(!q.empty())o<<q.top()<<" ",q.pop();return o;}
template<typename K,typename T>auto&operator<<(ostream&o,map<K,T>&m){for(auto&e:m)o<<e<<" ";return o;}
template<typename T>auto&operator<<(ostream&o,vector<T>v){for(auto&e:v)o<<e<<" ";return o;}
void ashow(){cout<<endl;}template<typename T,typename...A>void ashow(T t,A...a){cout<<t<<" ";ashow(a...);}
template<typename S,typename T,typename U>
struct TRI{S fi;T se;U th;TRI(){}TRI(S f,T s,U t):fi(f),se(s),th(t){}
bool operator<(const TRI&_)const{return(fi==_.fi)?((se==_.se)?(th<_.th):(se<_.se)):(fi<_.fi);}};
template<typename S,typename T,typename U>
auto&operator<<(ostream&o,TRI<S,T,U>&t){return o<<"{"<<t.fi<<","<<t.se<<","<<t.th<<"}";}

typedef pair<int, int> P;
typedef pair<ll,ll> pll;
typedef TRI<int, int, int> tri;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 100005;

#define getchar getchar_unlocked
#define putchar putchar_unlocked

inline int in() {
    int n = 0; short c;
    while ((c = getchar()) >= '0') n = n * 10 + c - '0';
    return n;
}

inline ll inll() {
    ll n = 0; short c;
    while ((c = getchar()) >= '0') n = n * 10 + c - '0';
    return n;
}

inline void out(ll n) {
    short res[20], i = 0;
    do { res[i++] = n % 10, n /= 10; } while (n);
    while (i) putchar(res[--i] + '0');
    putchar('\n');
}

template<typename T> class CHT {
private:
    struct node {
        node *left, *right;
        static const T inf = numeric_limits<T>::max();
        T a, b;
        node() : node(0, inf){}
        node(const T _a, const T _b)
            : left(nullptr), right(nullptr), a(_a), b(_b){}
        T f(const T x) const { return a * x + b; }
    };
    static void swap(node *x, node *y){
        std::swap(x->a, y->a), std::swap(x->b, y->b);
    }
    void _add_line(node *cur, node *nw, T l, T r){
        while(true){
            if(nw->f(l) < cur->f(l)) swap(cur, nw);
            if(cur->f(r - 1) <= nw->f(r - 1)) break;
            const T mid = (l + r) / 2;
            if(cur->f(mid) <= nw->f(mid)){
                if(!cur->right){
                    cur->right = new node(*nw);
                    break;
                }else{
                    cur = cur->right, l = mid;
                }
            }else{
                swap(cur, nw);
                if(!cur->left){
                    cur->left = new node(*nw);
                    break;
                }else{
                    cur = cur->left, r = mid;
                }
            }
        }
    }
    T query(node *cur, const T k, T l, T r) const {
        T ans = numeric_limits<T>::max();
        while(cur){
            ans = min(ans, cur->f(k));
            const T mid = (l + r) / 2;
            if(k < mid){
                cur = cur->left, r = mid;
            }else{
                cur = cur->right, l = mid;
            }
        }
        return ans;
    }
    void clear(node *cur){
        if(cur->left) clear(cur->left);
        if(cur->right) clear(cur->right);
        delete cur;
    }
    const T lpos, rpos;
    node *root;
public:
    CHT(const T _lpos, const T _rpos) : lpos(_lpos), rpos(_rpos), root(new node()){
        assert(lpos < rpos);
    }
    // ~CHT(){ clear(root); }
    // f(x) = a * x + b を挿入
    void add_line(const T a, const T b){
        node nw(a, b);
        return _add_line(root, &nw, lpos, rpos);
    }
    // x = k での最小値
    T query(const T k) const {
        return query(root, k, lpos, rpos);
    }
};

const ll MX = 1200000000000LL;
ll a[MAX_N], b[MAX_N];

int main(){
    int n = in(), C = in();
    CHT<ll> x(0, MX), y(0, n+1);
    rep(i,n) a[i+1] = inll(), b[i+1] = inll();
    ll p = 0, q = 0;
    x.add_line(0, 0);
    srep(i,1,n+1){
        p = x.query(a[i] + (ll)i * C) + b[i] + i * a[i] + ((ll)i * i - i) * C / 2;
        y.add_line(a[i] - (ll)i * C, p - (ll)i * a[i] + ((ll)i * i - i) * C / 2);
        q = y.query(i) + ((ll)i * i + i) * C / 2;
        x.add_line(-i, q + ((ll)i * i + i) * C / 2);
    }
    out(q);
    return 0;
}