#include <stdio.h>
#include <algorithm>
#include <vector>
#include <deque>
#include <string>
#include <iostream>
using namespace std;
using ll = long long;

void solve();
int main() {
	solve();
#ifdef DBG
	while (true);
#endif
}

//521
void solve() {
	int n, k;
	scanf("%d %d", &n, &k);

	if (k == 0 || n < k)
		printf("0\n");
	else
		printf("%d\n", n - 2 + (k * 2 - 1 == n));
}