import core.bitop;
import std.algorithm;
import std.ascii;
import std.bigint;
import std.conv;
import std.functional;
import std.math;
import std.numeric;
import std.range;
import std.stdio;
import std.string;
import std.random;
import std.typecons;
import std.container;

alias sread = () => readln.chomp();
long bignum = 1_000_000_007;

T lread(T = long)()
{
    return readln.chomp.to!T();
}

T[] aryread(T = long)()
{
    return readln.split.to!(T[])();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}

void main()
{
    long a, b, c, d;
    scan(a, b, c, d);
    long e = gcd(c, d);
    e = min(c, d) * (max(c, d) / e);
    long f = b / c - a / c + !(a % c);
    long g = b / d - a / d + !(a % c);
    long h = b / e - a / e + !(a % c);
    long i = f + g - h;
    (b - a - i + 1).max(0).writeln();
}
