Rsz a tech question

Hey everyone. I’m hoping someone can help me out. What does it mean when the R value starts at 0? Also, how do you figure out the msb bits for a lattice attack?

In elliptic curve digital signature algorithm (ECDSA), there are three (r,s,v) integers for every curve. The R [1...n-1] represents the x-coordinate on the elliptic curve based on a random point R on the curve which is created randomly thus results in starting with leading zero. ECDSA Signatures | Digital Signature Algorithms and Keys Generation