#include <bits/stdc++.h>
//#include "rainbow.h"
#define ll long long
#define ll1 long long
#define ull unsigned long long
#define dou long double
#define str string
#define vll vector<ll>
#define vi vector<int>
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vbool vector<bool>
#define vstr vector<str>
#define vvll vector<vll>
#define pb push_back
#define pf push_front
#define endl "\n"
#define fr first
#define se second
// #define sortcmp(a) sort(a.begin(), a.end(), cmp)
#define sort(a) sort(a.begin(), a.end())
#define reverse(a) reverse(a.begin(), a.end())
#define speed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define ordered_set tree<ll, null_type, less_equal<ll>, rb_tree_tag, tree_order_statistics_node_update>
using namespace std;
//using namespace __gnu_pbds;
const ll INF = 1e18;
const int lg = 20;
mt19937 rng(time(0));
ll randll(ll l, ll r){
return uniform_int_distribution<ll>(l, r)(rng);
}
int main(){
speed;
ll n, a, b;
cin >> n >> a >> b;
set<pll> s;
ll x = a;
if(a % 2 == 0) x /= 2;
ll res = 0;
vpll v;
//cout << INF << endl;
for(int i = 0; i < n; i ++){
ll l, r;
cin >> l >> r;
if(r-l+1 >= x){
cout << x << endl;
return 0;
}
v.pb({l%x, r%x});
if(v.back().se < v.back().fr){
pll p = v.back();
v.pop_back();
v.pb({p.fr, x-1});
v.pb({0, p.se});
}
/*for(auto j : v){
cout << j.fr << ' ' << j.se << endl;
}
cout << endl;*/
}
sort(v);
if(res != 0) cout << res << endl;
else{
ll l = v[0].fr, r = v[0].se;
for(int i = 0; i < v.size(); i ++){
//cout << v[i].fr << ' ' << v[i].se << endl;
if(v[i].fr <= r) r = max(r, v[i].se);
else{
res += r-l+1;
l = v[i].fr, r = v[i].se;
}
}
res += r-l+1;
cout << res << endl;
}
}
