//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define ld long double
#define rep(i, n) for(int i = 0; i < n; ++i)
#define rep2(i, a, b) for(int i = a; i <= b; ++i)
#define rrep(i, a, b) for(int i = a; i >= b; --i)
#define pii pair<int, int>
#define pll pair<ll, ll>
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define vi vector<int>
#define vll vector<ll>
#define vpii vector<pii>
#define vpll vector<pll>
#define vvi(a,b,c,d) vector<vector<int>> a(b,vector<int>(c,d));
#define vvll(a,b,c,d) vector<vector<ll>> a(b,vector<ll>(c,d));
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define endl '\n'
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
const int MOD = 1000000007;
//const int MOD=998244353;
const ll INF = 1e18+1;
const int inf = 1e9+1;
const double PI = acos(-1);
int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
int dy[8] = {0, 1, 0, -1, -1, 1, 1, -1};
bool range(int y, int x, int h, int w){
if(y < 0 || x < 0 || y >= h || x >= w) return false;
else return true;
}
const int MAX = 310000;
signed main(){
cin.tie(0);
ios::sync_with_stdio(false);
cout << fixed << setprecision(10);
ll n, m;
cin >> n >> m;
ll ans = 0;
rep2(i,1,1000000000){
ll bus = (n*i+m-1)/m;
chmax(ans, bus*m-n*i);
}
cout << ans << endl;
return 0;
}