// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")


#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;(i)<(n);(i)++)
#define REP(i,a,n) for(ll i=(a);(i)<(n);(i)++)
#define rrep(i,n) for(ll i=(n)-1;(i)>=(0ll);(i)--)
#define RREP(i,a,n) for(ll i=(n)-1;(i)>=(a);(i)--)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define be(v) (v).begin(),(v).end()
#define all(v) (v).begin(),(v).end()
#define foa(i,v) for(auto& (i) : (v))
#define UQ(v) sort(be(v)), (v).erase(unique(be(v)), (v).end())
#define UQ2(v,cmp) sort(be(v)), (v).erase(unique(be(v),cmp), (v).end())
#define UQ3(v,cmp) sort(be(v),cmp), (v).erase(unique(be(v)), (v).end())
#define UQ4(v,cmp,cmp2) sort(be(v), cmp), (v).erase(unique(be(v),cmp2), (v).end())
#define LB(x,v) (lower_bound(be(v),(x))-(v).begin())
#define LB2(x,v,cmp) (lower_bound(be(v),(x),(cmp))-(v).begin())
#define UB(x,v) (upper_bound(be(v),(x))-(v).begin())
#define UB2(x,v,cmp) (upper_bound(be(v),(x),(cmp))-(v).begin())
#define dout()  cout << fixed << setprecision(20)
#define randinit() srand((unsigned)time(NULL))

template<class T, class U> bool chmin(T& t, const U& u) { if (t > u){ t = u; return 1;} return 0; }
template<class T, class U> bool chmax(T& t, const U& u) { if (t < u){ t = u; return 1;} return 0; }


ll Rnd(ll L=0, ll R=mod99){return rand()%(R-L)+L;}

// 「Heavenly Me」 AIYUE blessed : Rina
void solve(){
    ll n,d;
    cin >> n >> d;
    V<pair<ll,ll>> a(n);
    rep(i,n){
        ll x,y;
        cin >>x >> y;
        a[i] = {y, x};
    }
    sort(be(a));
    reverse(be(a));
    V<ll> sv(n+1, 0);
    rep(i, n) sv[i+1] = sv[i] + a[i].second;
    
    ll ans = 0;
    ll D = 0;
    while(n > 0 and sv[n] > d){
        D = a[n-1].first;
        n--;
    }
    ans += D;
    V<pair<ll,ll>> b;
    rep(i, n){
        a[i].first -= D;
        ans += (a[i].first / d) * a[i].second;
        a[i].first %= d;
        b.eb(a[i].first, a[i].second);
    }
    sort(be(b));
    
    V<ll> sb(n+1, 0);
    rep(i, n) sb[i+1] = sb[i] + b[i].second;
    ll A = sb[n];
    rep(i, n) chmin(A, b[i].first + sb[n] - sb[i+1]);
    cout << ans + A << endl;
    
    
    
}

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t=1;
    // cin >> t;
    rep(i,t) solve();
}