import bisect
N,K=map(int,input().split())
A=[]
B=[]
for i in range(N):
    a,b=map(int,input().split())
    A.append(a)
    B.append(b+1)
    
C=A+B
D=set(C)
D=list(D)
D.sort()

F=[0 for i in range(len(D))]
for i in range(N):
    F[bisect.bisect_left(D,A[i])]+=1
    F[bisect.bisect_left(D,B[i])]-=1
E=[F[0]]
for i in range(1,len(F)):
    E.append(E[i-1]+F[i])
ans=0
#print(D)
#print(E)
for i in range(10**6):
    if (ans+E[i]*(D[i+1]-D[i]))>=K:
        if (K-ans)%E[i]==0:
            print(D[i]+(K-ans)//E[i]-1)
            exit()
        else:
            print(D[i]+(K-ans)//E[i])
            exit()
    else:
        ans+=(D[i+1]-D[i])*E[i]