use std::io::Write;
use std::collections::*;

type Map<K, V> = BTreeMap<K, V>;
type Set<T> = BTreeSet<T>;
type Deque<T> = VecDeque<T>;

fn main() {
    input! {
        n: usize,
        d: i64,
        p: [(i64, i64); n],
    }
    let mut p = p;
    p.sort_by_key(|p| p.1);
    let mut s = vec![0; n + 1];
    for i in (0..n).rev() {
        s[i] = s[i + 1] + p[i].0;
    }
    let mut memo = Map::new();
    let mut seg = SegmentTreePURQ::new(n, 0, |a, b| *a + *b);
    for (i, p) in p.iter().enumerate() {
        memo.entry(p.1 % d).or_insert(vec![]).push(i);
        seg.update(i, (p.1 + d - 1) / d * p.0);
    }
    let mut ans = p[n - 1].1;
    ans = ans.min(p.iter().map(|p| (p.1 + d - 1) / d * p.0).sum::<i64>());
    for (rem, pos) in memo {
        for x in pos {
            let p = p[x];
            seg.update(x, p.1 / d * p.0);
        }
        let mut l = 0;
        let mut r = 10i64.pow(9) * 2;
        while r - l > 1 {
            let m = (l + r) / 2;
            let x = p.upper_bound_by_key(&(m * d + rem), |p| p.1);
            if d > s[x] {
                r = m;
            } else {
                l = m;
            }
        }
        for &r in [l, r].iter() {
        let k = d * r + rem;
        let x = p.upper_bound_by_key(&(r * d + rem), |p| p.1);
        ans = ans.min(r * (d - s[x]) + rem + seg.find(x, n));
        }
    }
    println!("{}", ans);
}

/*

全体をK回やるとして

K + sum_{i, B_i >= K} A_i ceil((B_i - K) / D)
Bの昇順にソート

B0=0 として
B{i-1}<=K<=B_iの時、上の式
K mod D として考えるべきは B_j mod D (j>=i)の値
剰余固定すると？

K = qD + r

qD + r + sum_{i, B_i >= qD+r} A_i ceil((B_i - qD - r) / D)
sum_{i, B_i >= K} A_i (ceil((B_i - r) / D) - q)

q(D - sum_{i, B_i >= K} A_i) + r + sum_{i, B_i >= K} A_i ceil((B_i - r) / D)
二分探索できる形ではある、はず
実装がわからん


*/

// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
// ---------- begin super slice ----------
pub trait SuperSlice {
    type Item;
    fn lower_bound(&self, key: &Self::Item) -> usize
    where
        Self::Item: Ord;
    fn lower_bound_by<F>(&self, f: F) -> usize
    where
        F: FnMut(&Self::Item) -> std::cmp::Ordering;
    fn lower_bound_by_key<K, F>(&self, key: &K, f: F) -> usize
    where
        K: Ord,
        F: FnMut(&Self::Item) -> K;
    fn upper_bound(&self, key: &Self::Item) -> usize
    where
        Self::Item: Ord;
    fn upper_bound_by<F>(&self, f: F) -> usize
    where
        F: FnMut(&Self::Item) -> std::cmp::Ordering;
    fn upper_bound_by_key<K, F>(&self, key: &K, f: F) -> usize
    where
        K: Ord,
        F: FnMut(&Self::Item) -> K;
    fn next_permutation(&mut self) -> bool
    where
        Self::Item: Ord;
    fn next_permutation_by<F>(&mut self, f: F) -> bool
    where
        F: FnMut(&Self::Item, &Self::Item) -> std::cmp::Ordering;
    fn prev_permutation(&mut self) -> bool
    where
        Self::Item: Ord;
}

impl<T> SuperSlice for [T] {
    type Item = T;
    fn lower_bound(&self, key: &Self::Item) -> usize
    where
        T: Ord,
    {
        self.lower_bound_by(|p| p.cmp(key))
    }
    fn lower_bound_by<F>(&self, mut f: F) -> usize
    where
        F: FnMut(&Self::Item) -> std::cmp::Ordering,
    {
        self.binary_search_by(|p| f(p).then(std::cmp::Ordering::Greater))
            .unwrap_err()
    }
    fn lower_bound_by_key<K, F>(&self, key: &K, mut f: F) -> usize
    where
        K: Ord,
        F: FnMut(&Self::Item) -> K,
    {
        self.lower_bound_by(|p| f(p).cmp(key))
    }
    fn upper_bound(&self, key: &Self::Item) -> usize
    where
        T: Ord,
    {
        self.upper_bound_by(|p| p.cmp(key))
    }
    fn upper_bound_by<F>(&self, mut f: F) -> usize
    where
        F: FnMut(&Self::Item) -> std::cmp::Ordering,
    {
        self.binary_search_by(|p| f(p).then(std::cmp::Ordering::Less))
            .unwrap_err()
    }
    fn upper_bound_by_key<K, F>(&self, key: &K, mut f: F) -> usize
    where
        K: Ord,
        F: FnMut(&Self::Item) -> K,
    {
        self.upper_bound_by(|p| f(p).cmp(key))
    }
    fn next_permutation(&mut self) -> bool
    where
        T: Ord,
    {
        self.next_permutation_by(|a, b| a.cmp(b))
    }
    fn next_permutation_by<F>(&mut self, mut f: F) -> bool
    where
        F: FnMut(&Self::Item, &Self::Item) -> std::cmp::Ordering,
    {
        use std::cmp::Ordering::*;
        if let Some(x) = self.windows(2).rposition(|a| f(&a[0], &a[1]) == Less) {
            let y = self.iter().rposition(|b| f(&self[x], b) == Less).unwrap();
            self.swap(x, y);
            self[(x + 1)..].reverse();
            true
        } else {
            self.reverse();
            false
        }
    }
    fn prev_permutation(&mut self) -> bool
    where
        T: Ord,
    {
        self.next_permutation_by(|a, b| a.cmp(b).reverse())
    }
}
// ---------- end super slice ----------
// ---------- begin segment tree Point Update Range Query ----------
pub struct SegmentTreePURQ<T, F> {
    n: usize,
    size: usize,
    data: Vec<T>,
    e: T,
    op: F,
}

impl<T, F> SegmentTreePURQ<T, F>
where
    T: Clone,
    F: Fn(&T, &T) -> T,
{
    pub fn new(n: usize, e: T, op: F) -> Self {
        assert!(n > 0);
        let size = n.next_power_of_two();
        let data = vec![e.clone(); 2 * size];
        SegmentTreePURQ {
            n,
            size,
            data,
            e,
            op,
        }
    }
    pub fn update_tmp(&mut self, x: usize, v: T) {
        assert!(x < self.n);
        self.data[x + self.size] = v;
    }
    pub fn update_all(&mut self) {
        for i in (1..self.size).rev() {
            self.data[i] = (self.op)(&self.data[2 * i], &self.data[2 * i + 1]);
        }
    }
    pub fn update(&mut self, x: usize, v: T) {
        assert!(x < self.n);
        let mut x = x + self.size;
        self.data[x] = v;
        x >>= 1;
        while x > 0 {
            self.data[x] = (self.op)(&self.data[2 * x], &self.data[2 * x + 1]);
            x >>= 1;
        }
    }
    pub fn find(&self, l: usize, r: usize) -> T {
        assert!(l <= r && r <= self.n);
        if l == r {
            return self.e.clone();
        }
        let mut l = self.size + l;
        let mut r = self.size + r;
        let mut x = self.e.clone();
        let mut y = self.e.clone();
        while l < r {
            if l & 1 == 1 {
                x = (self.op)(&x, &self.data[l]);
                l += 1;
            }
            if r & 1 == 1 {
                r -= 1;
                y = (self.op)(&self.data[r], &y);
            }
            l >>= 1;
            r >>= 1;
        }
        (self.op)(&x, &y)
    }
    pub fn max_right<P>(&self, l: usize, f: P) -> usize
    where
        P: Fn(&T) -> bool,
    {
        assert!(l <= self.n);
        assert!(f(&self.e));
        if l == self.n {
            return self.n;
        }
        let mut l = l + self.size;
        let mut sum = self.e.clone();
        while {
            l >>= l.trailing_zeros();
            let v = (self.op)(&sum, &self.data[l]);
            if !f(&v) {
                while l < self.size {
                    l <<= 1;
                    let v = (self.op)(&sum, &self.data[l]);
                    if f(&v) {
                        sum = v;
                        l += 1;
                    }
                }
                return l - self.size;
            }
            sum = v;
            l += 1;
            l.count_ones() > 1
        } {}
        self.n
    }
    pub fn min_left<P>(&self, r: usize, f: P) -> usize
    where
        P: Fn(&T) -> bool,
    {
        assert!(r <= self.n);
        assert!(f(&self.e));
        if r == 0 {
            return 0;
        }
        let mut r = r + self.size;
        let mut sum = self.e.clone();
        while {
            r -= 1;
            while r > 1 && r & 1 == 1 {
                r >>= 1;
            }
            let v = (self.op)(&self.data[r], &sum);
            if !f(&v) {
                while r < self.size {
                    r = 2 * r + 1;
                    let v = (self.op)(&self.data[r], &sum);
                    if f(&v) {
                        sum = v;
                        r -= 1;
                    }
                }
                return r + 1 - self.size;
            }
            sum = v;
            (r & (!r + 1)) != r
        } {}
        0
    }
}
// ---------- end segment tree Point Update Range Query ----------