#include<bits/stdc++.h>

using namespace std;

#define fore(i, l, r) for(int i = int(l); i < int(r); i++)
#define sz(a) int((a).size())

#define x first
#define y second

typedef long long li;

li n, k;

inline bool read() {
    if(!(cin >> n >> k))
        return false;
    return true;
}

int getLen(li val) {
    int ans = 0;
    while(val > 0) {
        ans++;
        val >>= 1;
    }
    return ans;
}

li calcSize(li val, li mx) {
    if(val > mx)
        return 0;

    int diffLen = getLen(mx) - getLen(val);

    li ans = 0;
    fore(k, 0, diffLen)
        ans += 1ll << k;
    if(val > (mx >> diffLen))
        return ans;
    if(val < (mx >> diffLen))
        ans += 1ll << diffLen;
    else
        ans += mx - (val << diffLen) + 1;
    return ans;
}

li calcSubTree(li val, li mx) {
    if(val & 1ll)
        return calcSize(val, mx);
    return calcSize(val, mx) + calcSize(val + 1, mx);
}

inline void solve() {
    li lvl = 1;
    for(li curL = 1ll; curL <= n; curL <<= 1) {
        if(calcSubTree(curL, n) >= k)
            lvl = curL;
    }

    li ans = 0;

    li lf = lvl / 2, rg = lvl;
    while(rg - lf > 1) {
        li mid = (lf + rg) >> 1;
        if(calcSubTree(2 * mid, n) >= k)
            lf = mid;
        else
            rg = mid;
    }
    ans = max(ans, 2 * lf);

    lf = lvl / 2, rg = lvl;
    while(rg - lf > 1) {
        li mid = (lf + rg) >> 1;
        if(calcSubTree(2 * mid + 1, n) >= k)
            lf = mid;
        else
            rg = mid;
    }
    if(calcSubTree(2 * lf + 1, n) >= k)
        ans = max(ans, 2 * lf + 1);

    cout << ans << endl;
}

int main() {
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    int tt = clock();
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    cout << fixed << setprecision(15);

    if(read()) {
        solve();

#ifdef _DEBUG
        cerr << "TIME = " << clock() - tt << endl;
        tt = clock();
#endif
    }
    return 0;
}