#include <bits/stdc++.h>
using namespace std;

using S1 = long long;
class SegmentTree1{
    public:
    int siz = -1,n = -1;
    vector<S1> dat;
 
    S1 op(S1 a, S1 b){return a+b;}
    S1 e(){return 0;}
    void renew (S1 &a,S1 x){
        a = op(a,x);
        //a = x; //set(pos,x)で可能.
        //その他.
    }
 
    SegmentTree1(int N){init(N);}
    SegmentTree1(const vector<S1> &A){//長さ配列サイズに合わせる.
        siz = 1; n = A.size();
        while(siz < n) siz *= 2;
        dat.resize(siz*2,e());
        for(int i=0; i<n; i++) dat.at(i+siz) = A.at(i);
        for(int i=siz-1; i>0; i--) dat.at(i) = op(dat.at(i*2),dat.at(i*2+1));
    }
    void init(int N){
        //全要素単位元に初期化.
        siz = 1; n = N;
        while(siz < n) siz *= 2;
        dat.assign(siz*2,e());
    }
    void init(const vector<S1> &A){//長さ配列サイズに合わせる.
        siz = 1; n = A.size();
        while(siz < n) siz *= 2;
        dat.resize(siz*2,e());
        for(int i=0; i<n; i++) dat.at(i+siz) = A.at(i);
        for(int i=siz-1; i>0; i--) dat.at(i) = op(dat.at(i*2),dat.at(i*2+1));
    }
    void set(int pos,S1 x){
        pos = pos+siz;
        dat.at(pos) = x;
        while(pos != 1){
            pos = pos/2;
            dat.at(pos) = op(dat.at(pos*2),dat.at(pos*2+1));
        }
    }
    void update(int pos,S1 x){
        pos = pos+siz;
        renew(dat.at(pos),x);
        while(pos != 1){
            pos = pos/2;
            dat.at(pos) = op(dat.at(pos*2),dat.at(pos*2+1));
        }
    } 
    S1 findans(int l, int r){
        S1 retl = e(),retr = e();
        l += siz,r += siz;
        while(l < r){
            if(l&1) retl = op(retl,dat.at(l++));
            if(r&1) retr = op(dat.at(--r),retr);
            l >>= 1; r >>= 1;
        }
        return op(retl,retr);
    }
    S1 get(int pos){return dat.at(pos+siz);}
    S1 rangeans(int l, int r){return findans(l,r);}
    S1 allrange(){return dat.at(1);}
 
    //rightは) leftは[で 渡す&返す. 
    int maxright(const function<bool(S1)> f,int l = 0){
        //fを満たさない最小の箇所を返す なければn.
        l += siz; int r = n+siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        S1 okl = e();
        for(int i=0; i<ls.size(); i++){
            l = ls.at(i);
            S1 now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        for(int i=rs.size()-1; i>=0; i--){
            l = rs.at(i);
            S1 now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        return n;
    }
    int minleft(const function<bool(S1)> f,int r = -1){
        //fを満たす最小の箇所を返す なければ0.
        if(r == -1) r = n;
        int l = siz; r += siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        S1 okr = e();
        for(int i=0; i<rs.size(); i++){
            r = rs.at(i);
            S1 now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
            okr = now;
        }
        for(int i=ls.size()-1; i>=0; i--){
            r = ls.at(i);
            S1 now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
            okr = now;
        }
        return 0;
    }
};

using S2 = pair<long long,long long>;
class SegmentTree2{
    public:
    int siz = -1,n = -1;
    vector<S2> dat;
 
    S2 op(S2 a, S2 b){return {min(a.first,b.first+a.second),a.second+b.second};}
    S2 e(){return {0,0};}
    void renew (S2 &a,S2 x){
        a = op(a,x);
        //a = x; //set(pos,x)で可能.
        //その他.
    }
 
    SegmentTree2(int N){init(N);}
    SegmentTree2(const vector<S2> &A){//長さ配列サイズに合わせる.
        siz = 1; n = A.size();
        while(siz < n) siz *= 2;
        dat.resize(siz*2,e());
        for(int i=0; i<n; i++) dat.at(i+siz) = A.at(i);
        for(int i=siz-1; i>0; i--) dat.at(i) = op(dat.at(i*2),dat.at(i*2+1));
    }
    void init(int N){
        //全要素単位元に初期化.
        siz = 1; n = N;
        while(siz < n) siz *= 2;
        dat.assign(siz*2,e());
    }
    void init(const vector<S2> &A){//長さ配列サイズに合わせる.
        siz = 1; n = A.size();
        while(siz < n) siz *= 2;
        dat.resize(siz*2,e());
        for(int i=0; i<n; i++) dat.at(i+siz) = A.at(i);
        for(int i=siz-1; i>0; i--) dat.at(i) = op(dat.at(i*2),dat.at(i*2+1));
    }
    void set(int pos,S2 x){
        pos = pos+siz;
        dat.at(pos) = x;
        while(pos != 1){
            pos = pos/2;
            dat.at(pos) = op(dat.at(pos*2),dat.at(pos*2+1));
        }
    }
    void update(int pos,S2 x){
        pos = pos+siz;
        renew(dat.at(pos),x);
        while(pos != 1){
            pos = pos/2;
            dat.at(pos) = op(dat.at(pos*2),dat.at(pos*2+1));
        }
    } 
    S2 findans(int l, int r){
        S2 retl = e(),retr = e();
        l += siz,r += siz;
        while(l < r){
            if(l&1) retl = op(retl,dat.at(l++));
            if(r&1) retr = op(dat.at(--r),retr);
            l >>= 1; r >>= 1;
        }
        return op(retl,retr);
    }
    S2 get(int pos){return dat.at(pos+siz);}
    S2 rangeans(int l, int r){return findans(l,r);}
    S2 allrange(){return dat.at(1);}
 
    //rightは) leftは[で 渡す&返す. 
    int maxright(const function<bool(S2)> f,int l = 0){
        //fを満たさない最小の箇所を返す なければn.
        l += siz; int r = n+siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        S2 okl = e();
        for(int i=0; i<ls.size(); i++){
            l = ls.at(i);
            S2 now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        for(int i=rs.size()-1; i>=0; i--){
            l = rs.at(i);
            S2 now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        return n;
    }
    int minleft(const function<bool(S2)> f,int r = -1){
        //fを満たす最小の箇所を返す なければ0.
        if(r == -1) r = n;
        int l = siz; r += siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        S2 okr = e();
        for(int i=0; i<rs.size(); i++){
            r = rs.at(i);
            S2 now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
            okr = now;
        }
        for(int i=ls.size()-1; i>=0; i--){
            r = ls.at(i);
            S2 now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
            okr = now;
        }
        return 0;
    }
};

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,D; cin >> N >> D;
    vector<pair<long long,long long>> BA(N);
    for(auto &[b,a] : BA) cin >> a >> b;
    sort(BA.rbegin(),BA.rend());
    BA.push_back({0,0});

    vector<long long> X;
    for(auto [b,a] : BA) X.push_back(b%D);
    sort(X.begin(),X.end());
    X.erase(unique(X.begin(),X.end()),X.end());
    int n = X.size();
    for(int i=0; i<n; i++) X.push_back(X.at(i)+D);

    SegmentTree1 Z(n+n);
    vector<S2> give(n+n);
    for(int i=1; i<n+n; i++){
        auto &[d,s] = give.at(i); 
        d = 0,s = X.at(i)-X.at(i-1);
    }
    SegmentTree2 Z2(give);
    long long answer = BA.at(0).first,suma = 0,now = 0;
    for(int i=0; i<N; i++){
        auto [b,a] = BA.at(i);
        auto [b2,a2] = BA.at(i+1);
        if(i){
            long long add = b-b2;
            now += suma*(add/D),add %= D;
            if(add){
                int l = b2%D,r = b%D;
                l = lower_bound(X.begin(),X.end(),l)-X.begin();
                r = lower_bound(X.begin(),X.end(),r)-X.begin();
                if(l > r) r += n;
                now += Z.rangeans(l+1,r+1);
            }
        }

        int pos = lower_bound(X.begin(),X.end(),b%D)-X.begin();
        Z.update(pos,a),Z.update(pos+n,a),suma += a,now += (b-b2+D-1)/D*a;
        if(suma >= D) break;
        
        auto [dec,sum] = Z2.get(pos);
        dec -= a,sum -= a;
        Z2.set(pos,{dec,sum}),Z2.set(pos+n,{dec,sum});
        pos = lower_bound(X.begin(),X.end(),b2%D)-X.begin();
        tie(dec,sum) = Z2.rangeans(pos+1,pos+n);
        dec += X.at(pos+1)-X.at(pos);
        answer = min(answer,now+b2+min(0LL,dec));
    }
    
    cout << answer << endl;
}