#include <iostream>
#include <queue>

using namespace std;

queue<int> q;
int dist[100001];
bool check[100001];
int A, B, N, M;

bool isInB(int n) {
    if(n >= 0 && n <= 100000)
        return true;
    else
        return false;
}

void pushNext(int now) {
    int nextDist = dist[now] + 1;
    if(isInB(now+1))
        if(!check[now+1]) {
            q.push(now+1);
            dist[now+1] = nextDist;
            check[now+1] = true;
        }

    if(isInB(now-1))
        if(!check[now-1]) {
            q.push(now-1);
            dist[now-1] = nextDist;
            check[now-1] = true;
        }

    if(isInB(now+A))
        if(!check[now+A]) {
            q.push(now+A);
            dist[now+A] = nextDist;
            check[now+A] = true;
        }

    if(isInB(now-A))
        if(!check[now-A]) {
            q.push(now-A);
            dist[now-A] = nextDist;
            check[now-A] = true;
        }

    if(isInB(now+B))
        if(!check[now+B]) {
            q.push(now+B);
            dist[now+B] = nextDist;
            check[now+B] = true;
        }

    if(isInB(now-B))
        if(!check[now-B]) {
            q.push(now-B);
            dist[now-B] = nextDist;
            check[now-B] = true;
        }

    if(isInB(now*A))
        if(!check[now*A]) {
            q.push(now*A);
            dist[now*A] = nextDist;
            check[now*A] = true;
        }

    if(isInB(now*B))
        if(!check[now*B]) {
            q.push(now*B);
            dist[now*B] = nextDist;
            check[now*B] = true;
        }
}

int main()
{
    cin >> A >> B >> N >> M;

    check[N] = true;
    dist[N] = 0;

    q.push(N);
    while(!q.empty()) {
        int now = q.front(); q.pop();
        if(now == M)
           break;

        pushNext(now);
    }

    cout << dist[M] << endl;
}