"use strict";

const main = arg => {
    const input = arg.trim().split("\n");

    let A = parseInt(input[0].split(" ")[0]);
    const B = parseInt(input[0].split(" ")[1]);
    let C = parseInt(input[0].split(" ")[2]);
    const D = parseInt(input[0].split(" ")[3]);

    while(true){
        C=C-B
        if(C<=0){
            console.log("Yes")
            return
        }
        A = A - D
        if(A<=0){
            console.log("No")
            return
        }
    }
    
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));  