#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

char*mmap();
#define RD(v) int v=0;{int _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}

#define WTHI(v) {long _z=v,_n=0,_d=0;while(++_n,_d=_d<<8|0x30|_z%10,_z/=10);*(long*)wp=_d;wp+=_n;}
#define WTLO(v) {long _z=v,_n=8,_d=0;while(_d=_d<<8|0x30|_z%10,_z/=10,--_n);*(long*)wp=_d;wp+=8;}
#define WT(v) if(v>=100000000){WTHI(v/100000000);WTLO(v);}else{WTHI(v);}

void radix_sort_aux(unsigned*a,unsigned*b,int n,int d){
	int c[256];
	for(int i=0;i<256;++i){
		c[i]=0;
	}
	for(int i=0;i<n;++i){
		++c[a[i]>>d&255];
	}
	int t=0;
	for(int i=0;i<256;++i){
		int u=c[i];
		c[i]=t;
		t+=u;
	}
	for(int i=0;i<n;++i){
		b[c[a[i]>>d&255]++]=a[i];
	}
}

void radix_sort(unsigned*a,int n){
	radix_sort_aux(a,a+n,n,0);
	radix_sort_aux(a+n,a,n,8);
	radix_sort_aux(a,a+n,n,16);
	radix_sort_aux(a+n,a,n,24);
}

unsigned as[400000];

main(){
	char*rp=mmap(0l,11l*200003,1,2,0,0ll);
	RD(n);
	RD(k);
	for(int i=0;i<n;++i){
		RD(a);
		as[i*2+0]=a*2+1;
		RD(b);
		as[i*2+1]=b*2+2;
	}
	radix_sort(as,n*2);
	long p=1,d=0,s=0;
	int i=0;
	for(;;++i){
		long a=as[i];
		s+=((a>>1)-p)*d;
		if(s>=k) break;
		p=a>>1;
		d+=a&1?:-1;
	}
	long z=(as[i]>>1)-(s-k)/d-1;
	char wbuf[16],*wp=wbuf;
	WT(z);
	write(1,wbuf,wp-wbuf);
	_exit(0);
}