#include<bits/stdc++.h>
#define inf 0x7f7f7f7f
using namespace std;
typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
inline int read()
{
    int x=0,f=1;char ch=getchar();
    for (;ch<'0'||ch>'9';ch=getchar())  if (ch=='-')    f=-1;
    for (;ch>='0'&&ch<='9';ch=getchar())    x=(x<<1)+(x<<3)+ch-'0';
    return x*f;
}
inline void print(int x)
{
    if (x>=10)     print(x/10);
    putchar(x%10+'0');
}
const int N=2e3;
int val[N+10];
int main()
{
    int n=read(),have=read(),remain=read(),date=read();
    for (int i=1;i<=n;i++)
	{
        int l=read(),r=read();
        val[l]++,val[r+1]--;
    }
    for (int i=1;i<=date;i++)   val[i]=val[i]+val[i-1];
    int sum=have-remain;
    for (int i=date;i>=1;i--)
	{
        sum-=val[i];
        if (!sum)
		{
            printf("%d\n",i);
            break;
        }
    }
    return 0;
}