import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
bool minimize(T)(ref T x, T y) { if (x > y) { x = y; return true; } else { return false; } }
bool maximize(T)(ref T x, T y) { if (x < y) { x = y; return true; } else { return false; } }

long mod = 10^^9 + 7;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{	
	auto N = RD;
	auto K = RD;
	auto ab = new long[2][](N);
	long[long] s;
	foreach (i; 0..N)
	{
		auto A = RD;
		auto B = RD+1;
		ab[i] = [A, B];
		++s[A<<1];
		++s[(B<<1)+1];
	}

	debug writeln();
	long ans;
	long vol, cnt, last;
	foreach (key; s.keys.sort())
	{
		auto x = key >> 1;
		debug writeln(x, " ", s[key]);
		cnt += (x - last) * vol;
		debug writeln(cnt);
		
		if (cnt >= K)
		{
			auto diff = cnt - K;
			debug writeln(diff, " ", vol,  " ", diff % vol);
			ans = x - (diff / vol) - 1;
			break;
		}

		last = x;
		if (key % 2 == 1)
		{
			vol -= s[key];
		}
		else
		{
			vol += s[key];
		}
	}

	writeln(ans);
	stdout.flush();
	debug readln();
}