//  [java]
import java.io.IOException;
import java.io.InputStream;
import java.util.NoSuchElementException;

public class Main {

	public static void main(String[] args) throws ClassNotFoundException, IOException {
		FastScanner sc = new FastScanner();
		long A = sc.nextLong();
		long B = sc.nextLong();
		long C = sc.nextLong();
		long D = sc.nextLong();

		long numBC = B / C;
		long numAC = A / C;
		long numCbaisu = numBC - numAC;
		if(A % C == 0) {
			numCbaisu++;
		}
		long numBD = B / D;
		long numAD = A / D;
		long numDbaisu = numBD - numAD;
		if(A % D == 0) {
			numDbaisu++;
		}
		long saisyoukoubai = lcm(C, D);
		long numBsaisyou = B / saisyoukoubai;
		long numAsaisyou = A / saisyoukoubai;
		long numCDbaisu = numBsaisyou - numAsaisyou;
		if(A % saisyoukoubai == 0) {
			numCDbaisu++;
		}

		long sumNum = B - A + 1;

		long answer = sumNum - (numCbaisu + numDbaisu - numCDbaisu);
		if(answer < 0) {
			System.out.println(0);
		}else {
			System.out.println(sumNum - (numCbaisu + numDbaisu - numCDbaisu));
		}

	}

	static long lcm (long a, long b) {
		long temp;
		long c = a;
		c *= b;
		while((temp = a%b)!=0) {
			a = b;
			b = temp;
		}
		return (long)(c/b);
	}
}

class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
    public double nextDouble() { return Double.parseDouble(next());}
}