Codeforces Round #268 (Div. 2), problem: (B) Chat Online

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define pii pair<int,int>
#define pli pair<long long int,int>
#define pbi pair<bool,int>
#define pob pop_back
#define all(a) a.begin(),a.end()
#define fio ios_base::sync_with_stdio(false); cin.tie(NULL);cout.tie(NULL);
#define i64 long long int
#define mem(x,y) memset(x,y,sizeof(x))
#define fill(arr,b) fill(arr, arr+sizeof(arr)/sizeof(arr[0]), b)
#define maxarr(n,arr,m) m=-1e9;for(int i=0;i<n;i++)if(arr[i]>m) m=arr[i];
#define read freopen("input.txt","r",stdin);
#define sortd(x,y) sort(x,y,greater<int>());
#define F first
#define S second

const int maxn = (i64)1e9+7;
const double pi = acos(-1.0);

//bool fne(const pii &a, const pii &b){return (a.F > b.F)||(a.F==b.F&&a.S>b.S);}
//bool sne(const pii &a, const pii &b){return (a.S < b.S)||(a.S==b.S&&a.F<b.F);}
//bool isprime(int n){for(int i=2;i*i<=n;i++){if(n%i==0)return false;}return true;}


int main(){
    fio;
    int p,q,l,r;
    cin>>p>>q>>l>>r;
    int a,b;
    bitset<2005>bs1,bs2;
    while(p--){
        cin>>a>>b;
        while(a<=b){
            bs1[a]=1;
            a++;
        }
    }
    while(q--){
        cin>>a>>b;
        while(a<=b){
            bs2[a]=1;
            a++;
        }
    }
    int ans=0;
    for(;l<=r;l++)
        if((bs1&bs2<<l).count()) ans++;
    cout<<ans;

    return 0;
}