#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

ll gcd(ll a, ll b){return (b==0?a:gcd(b,a%b));}
ll lcm(ll a, ll b){return a/gcd(a,b)*b;}

int main(){
  ios::sync_with_stdio(false);
  ll N, D;
  cin >> N >> D;

  if(gcd(N,D)==1){
    cout << N-1 << endl;
  }else{
    cout << lcm(N,D)/D-1 << endl;
  }
  
  return 0;
}