【题目链接】:http://codeforces.com/contest/787/problem/A

【题意】



把b一直加a->得到x

把d一直加c->得到y

然后问你x和y可不可能有相同的值.

有的话,输出那个最小的;

【题解】



等价于

令t=(b+u*a-d)%c==0

u为整数

这里如果b< d就swap(a,c),swap(b,d)就好;

然后如果t遇到了重复的值,就结束,往后都不可能了;

如果t中途变成0了,就输出那个u;



【完整代码】

#include <bits/stdc++.h>

using namespace std;

#define lson l,m,rt<<1

#define rson m+1,r,rt<<1|1

#define LL long long

#define rep1(i,a,b) for (int i = a;i <= b;i++)

#define rep2(i,a,b) for (int i = a;i >= b;i--)

#define mp make_pair

#define pb push_back

#define fi first

#define se second

#define rei(x) scanf("%d",&x)

#define rel(x) scanf("%lld",&x)

#define ref(x) scanf("%lf",&x)

typedef pair<int, int> pii;

typedef pair<LL, LL> pll;

const int dx[9] = { 0,1,-1,0,0,-1,-1,1,1 };

const int dy[9] = { 0,0,0,-1,1,-1,1,-1,1 };

const double pi = acos(-1.0);

const int N = 110;

map <int, int> dic;

int a, b, c, d;

int ans = -1;

void in()

{

    rei(a), rei(b);

    rei(c), rei(d);

}

int get_ans()

{

    int x = 0;

    if (b < d)

    {

        swap(a, c);

        swap(b, d);

    }

    //b>=d

    int t = (b + x*a - d) % c;

    while (t != 0)

    {

        if (dic[t])

            return -1;

        dic[t] = 1;

        x++;

        t = (b + x*a - d) % c;

    }

    return x;

}

int main()

{

    //freopen("F:\\rush.txt", "r", stdin);

    in();

    ans = get_ans();

    if (ans==-1)

        puts("-1");

    else

        printf("%d\n",b+ans*a);

    //printf("\n%.2lf sec \n", (double)clock() / CLOCKS_PER_SEC);

    return 0;

}