"use strict";
    
const main = arg => {
    arg = arg.trim().split("\n");
    let A = parseInt(arg[0].split(" ")[0]);
    const B = parseInt(arg[0].split(" ")[1]);
    let C = parseInt(arg[0].split(" ")[2]);
    const D = parseInt(arg[0].split(" ")[3]);
    
    let i = 0;
    
    while(A > 0 && C > 0) {
        if(i % 2 === 0) {
            C -= B;
        } else {
            A -= D;
        }
        i++;
    }
    
    if(A > C) {
        console.log("Yes");
    } else {
        console.log("No");
    }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));