This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<bits/stdc++.h>
 
 
 
using namespace std;
 
 
 
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
 
 
 
#define str string
#define append push_back
#define vector deque
#define vi vector<int>
#define int long long
#define yes cout<<"YES"<<endl;
#define no cout<<"NO"<<endl;
#define endl '\n'
#define all(ls) ls.begin(),ls.end()
#define sorted(ls) sort(ls.begin(),ls.end());
#define reversed(ls) reverse(ls.begin(),ls.end());
#define print(n) for(auto i:n)cout<<i<<' ';cout<<endl;
#define input(n,ls,m) deque<n>ls(m);for(int i=0;i<m;i++)cin>>ls[i];
#define len(s) s.size()
#define ff first
#define ss second
#define N (int const) 3e5+1
#define pii pair<int,int>
#define SQ(x) ((x)*(x))
#define float double
 
 
int mod=1e9+7;
int mod1=998244353;
 
 
 
int sum_(vector<int>ls){int s=0;for(auto i:ls){s+=i;}return s;}
int min(int a,int b){if (a>b){return b;}return a;}
int max(int a,int b){if (a<b){return b;}return a;}
 
 
 
//......................................tHe ReaL cOdE beGinS HerE....................................../
 
void solve(){
    int n,a,b;;
    cin>>n>>a>>b;
    vector<pii>ls;
    for(int i=0;i<n;i++){
        int x,y;
        cin>>x>>y;
        ls.append({x,y});
    }
    a/=gcd(a,b+1);
    if((int)(log(a)+log(b))>=18){
        int ans=0;
        for(auto i:ls){
            ans+=i.ss-i.ff+1;
        }
        cout<<ans<<endl;return;
    }
    a*=b;
    for(auto i:ls){
        if(i.ss-i.ff+1>=a){
            cout<<a<<endl;return;
        }
    }
    vector<pii>q;
    for(auto i:ls){
        int f=i.ff%a,s=i.ss%a;
        if(f<s or i.ff==i.ss) q.append({f,s});
        else{
            q.append({f,a-1});
            q.append({0,s});
        }
    }
    sorted(q);
    int ans=a-q[0].ff;
    int maxi=0;
    for(int i=1;i<q.size();i++){
        if(q[i-1].ss<q[i].ff){
            ans-=q[i].ff-q[i-1].ss-1;
        }
        maxi=max(maxi,q[i].ss);
    }
    cout<<ans-(a-maxi-1)<<endl;
}
 
 
 
 
 
signed main(){
    int t=1;
    // cin>>t;
    while(t--)
        solve();
}
Compilation message (stderr)
strange_device.cpp: In function 'void solve()':
strange_device.cpp:88:18: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::deque<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   88 |     for(int i=1;i<q.size();i++){
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