#include <stdio.h>
#include <string>
#include <cstring>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <list>
#include <iterator>
#pragma warning(disable:4996)
 
typedef long long ll;
#define MIN(a, b) ((a)>(b)? (b): (a))
#define MAX(a, b) ((a)<(b)? (b): (a))
#define LINF 9223300000000000000
#define INF 2140000000
#define MOD 1000000007
using namespace std;

int main(int argc, char* argv[])
{
    long n, k;
    scanf("%ld%ld", &n, &k);

    map<long, long> cnt;
    long i;
    for(i=0; i<n; i++) {
        long a,b;
        scanf("%ld%ld", &a, &b);
        cnt[a-1]++;
        cnt[b]--;
    }

    ll sum=0;
    long val_prev=0;
    long prev=0;
    auto it=cnt.begin();
    ll ans=0;
    for(; it!=cnt.end(); ++it) {
        if(it!=cnt.begin()) {
            sum += val_prev * (it->first-prev);
            if(sum>k) break;
        }
        val_prev+=it->second;
        prev=it->first;
        if(val_prev>0) ans = prev+(k-sum-1)/val_prev;
    }
    printf("%lld\n", ans+1);

    return 0;
}