#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, a, b, ans=0, low=LLONG_MIN/2, high=LLONG_MIN/2-1;
cin>>n>>a>>b;
__int128 m=a/gcd(a, b+1)*b;
set<pii> s;
while (n--){
cin>>a>>b;
if (b-a+1>=m){
cout<<(int)m;
return 0;
}
a%=m, b%=m;
if (a<=b)s.insert(mp(a, b));
else s.insert(mp(0, b)), s.insert(mp(a, m-1));
}
for (auto it=s.begin(); it!=s.end(); ++it){
if (it->fi<=high)high=max(high, it->se);
else ans+=high-low+1, low=it->fi, high=it->se;
}
cout<<ans+high-low+1;
}
