// yukicoder: No.817 Coin donation
// 2019.6.16 bal4u

#include <stdio.h>

#if 1
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int in() {   // 非負整数の入力
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf); while ((c = gc()) >= '0');
	return n;
}

#define INF 1000000000
typedef struct { int a, b; } T;
T t[100005];

int main()
{
	int i, N, K, s;
	int l, r, m;

	N = in(), K = in();
	for (i = 0; i < N; i++) t[i].a = in(), t[i].b = in();

	// バイナリサーチ
    l = 0, r = INF;
    while (l < r) {
		m = (l + r) >> 1, s = 0;
		for (i = 0; i < N; i++) if (t[i].a <= m) {
			if (t[i].b <= m) s += t[i].b - t[i].a + 1;
			else s += m - t[i].a + 1;
			if (s > K) break;
		}
		if (s == K) { l = m; break; }
		if (s < K) l = m+1; else r = m;
    }
    printf("%d\n", l);
	return 0;
}