import std;

bool calc(int a, int b, int c, int d) {
    int x = (c + b - 1) / b;
    int y = (a + d - 1) / d;
    return x <= y;
}

void main() {
    int a, b, c, d; scan(a, b, c, d);
    writeln(calc(a, b, c, d) ? "Yes" : "No");
}

void scan(T...)(ref T a) {
    string[] ss = readln.split;
    foreach (i, t; T) a[i] = ss[i].to!t;
}
T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;
