数学/Codeforces 483b Friends and Presents

 1 #include<cstdio>
 2 using namespace std;
 3 long long m,cnt1,cnt2,x,y;
 4 long long gcd(long long a,long long b)
 5 {
 6     if (b==0) return a;
 7     return gcd(b,a % b);
 8 }
 9 long long lcm(long long a,long long b)
10 {
11     return a*b/gcd(a,b);
12 }
13 bool f(long long n)
14 {
15     long long xx=n-n/x,yy=n-n/y;
16     if (xx<cnt1 || yy<cnt2) return false;
17     long long both=n/m;
18     if ((n-both)<cnt1+cnt2) return false;
19     return true;
20 }
21 int main()
22 {
23     scanf("%lld%lld%lld%lld",&cnt1,&cnt2,&x,&y);
24     m=lcm(x,y);
25     long long l=1,r=1e10;
26     while (l<r)
27     {
28         long long mid=(l+r)/2;
29         if (f(mid)) r=mid;
30         else l=mid+1;
31     }
32     printf("%lld\n",r);
33     return 0;
34 }