import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //
void solve(){
	long a = read.to!long;
	long b = read.to!long;
	long c = read.to!long;
	long d = read.to!long;
	
	long m = (c / gcd(c, d)) * d;
	log("m:", m);
	
	long bx = b - b / c - b / d + b / m;
	long ax = (a - 1) - (a - 1) / c - (a - 1) / d + (a - 1) / m;
	log("ax:", ax, "bx:", bx);
	
	long ans = bx - ax;
	
	ans.writeln;
}

long gcd(long a, long b){
	if(a % b == 0) return b;
	if(a < b) return gcd(b, a);
	else return gcd(b, a % b);
}
long lcm(long a, long b){
	return (a / gcd(a, b) * b);
}

