#include "bits/stdc++.h"
using namespace std;
#define fastcin {\
    cin.tie(0);\
    ios::sync_with_stdio(false);\
}
#define rep(i, a, b) for(int i = a; i < b; i++)
#define rrep(i, a, b) for(int i = a; i >= b; i--)
#define fore(i, a) for(auto &i:a)
#define print(x) cout << x << "\n"
#define SORT(a, n) sort(a, a+n);
#define REVERSE(a,n) reverse(a,a+n);
#define VSORT(v) sort(v.begin(), v.end());
#define VREVERSE(v) reverse(v.begin(), v.end());
#define MOD 1000000007
#define yes "YES"
#define no "NO"
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vll = vector<ll>;

ll combination(int n,int r) { 
    ll i = 1; 
    int k = r > n - r ? n - r : r, count; 
    if(k < 0) return 0; 
    std::list<int> list; 
    std::list<int>::iterator it; 
    for(count = 2; count <= k; ++count) list.push_back(count); 
    for(count = n; count > n - k; --count) 
    { 
        i *= count; 
        for(it = list.begin(); it != list.end(); ) 
        { 
            if(!(i % *it)) 
            { 
                i /= *it; 
                it = list.erase(it); 
            } 
            else ++it; 
        } 
    } 
    return i; 
} 

int main() {
    fastcin;
    int n, k, ans = 0;
    cin >> n >> k;
    if(k == 0 || k > n);
    else if(n < 3);
    else if(n&1 && n/2==k-1) ans = n-1;
    else ans = n-2;
    print(ans);
    return 0;
}