function main(input) {
    const args = input.split(' ');
    let a = parseInt(args[0], 10);
    let b = parseInt(args[1], 10);
    let c = parseInt(args[2], 10);
    let d = parseInt(args[3], 10);

    for (let i = 0; i <= 100; i++) {
        c -= b;
        if (c <= 0) {
            console.log('Yes');
            break
        }
        a -= d;
        if (a <= 0) {
            console.log('No');
            break
        }
    }
}

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