#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>

using namespace std;
using namespace __gnu_pbds;

template<typename T>
ostream_iterator<T> oit(const string &s = " "){ return ostream_iterator<T>(cout,s.c_str()); }
inline auto rep(int l, int r) { return views::iota(min(l, r), r); }
inline auto rep(int n) { return rep(0, n); }
inline auto rep1(int l, int r) { return rep(l, r + 1); }
inline auto rep1(int n) { return rep(1, n + 1); }
inline auto per(int l, int r) { return rep(l, r) | views::reverse; }
inline auto per(int n) { return per(0, n); }
inline auto per1(int l, int r) { return per(l, r + 1); }
inline auto per1(int n) { return per(1, n + 1); }
#define A(a) begin(a),end(a)
inline auto len = ranges::ssize;

struct chash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
template<typename T, typename U> using pb_map = gp_hash_table<T, U, chash>;
template<typename T> using pb_set = gp_hash_table<T, null_type, chash>;
#define K first
#define V second

using ll = long long;
using ld = long double;

using vi = vector<int>;
using vii = vector<vector<int>>;
typedef vector<ll> vll;
using pll = pair<ll,ll>;
using pii = pair<int,int>;

constexpr ll NN = 2e5, L = 20;

ll M;
ll f1[NN], f2[NN];
ll inv(ll a, ll b=M) { return 1 < a ? b - inv(b % a, a) * b / a : 1; } // inv a mod b
ll choose(ll n, ll k) { return f1[n] * f2[k] % M * f2[n - k] % M; } // n choose k


ll powmod(ll x, ll y){
  if(y==0) return 1LL;
  ll t=powmod(x,y/2);
  if (y%2==0) return (t*t)%M;
  return (((x*t)%M)*t)%M;
}


void run()
{
    ll s1,m1,s2,m2;
    cin >> s1 >> m1 >> s2 >> m2;

    for(ll i : rep1(10000)){
        s1 += 1, s1 %= m1;
        s2 += 1, s2 %= m2;
        if(s1 == s2 and s1==0)
            return void(cout << i << '\n');
    }
    assert(false);
}

int main()
{
    //KING OF THE WORLD...... U.W.T.B
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    run();
}