C++ :

#include <stdio.h>
int main()
{
	//freopen( "in.txt" , "r" , stdin ) ;
	//freopen( "out.txt" , "w" , stdout ) ;

 	int n , m ;
 	while( ~scanf ( "%d%d" , &n , &m ) ) {
        if( m % n == 0 ) printf( "%d\n" , n - 1)  ;
		 else printf( "%d\n" , m % n - 1 ) ;
	 }
	return 0 ;
}