'use strict'

function main(input) {
    let a = Number(input.split('\n')[0].split(' ')[0]);
    let b = Number(input.split('\n')[0].split(' ')[1]);
    let c = Number(input.split('\n')[0].split(' ')[2]);
    let d = Number(input.split('\n')[0].split(' ')[3]);
    let count1 = 0;
    let count2 = 0;
    while(1) {
        if ((c - b) > 0) {
            count1++;
            c = c - b;
        } else {
            break;
        }
    }
    while(1) {
        if ((a - d) > 0) {
            count2++;
            a = a - d;
        } else {
            break;
        }
    }
    if (count1 <= count2) {
        console.log('Yes');
    } else {
        console.log('No');
    }
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));