How it execute a 515 output?

Question

Union a have a non declaring variable ie int i..
But how it makes u.i 515 within the printf function???

https://code.sololearn.com/c25XYMW4wQou/?ref=app
#include<stdio.h>
int main()
{
union a { int i; char ch[2]; };
union a u; u.ch[0]=3; u.ch[1]=2;
printf("%d, %d, %d", u.ch[0], u.ch[1], u.i);
return 0; }

Answer 1

Sir where from the 256 came to this equation?