process.stdin.resume();
process.stdin.setEncoding('utf8');
var lines = [];
var reader = require('readline').createInterface({
    input: process.stdin,
    output: process.stdout,
    terminal: false
});
reader.on('line', (line) => {
    lines.push(line);
});
reader.on('close', () => {
    let [lifeA, atkA, lifeB, AtkB] = lines[0].split(" ").map(e => parseInt(e));
    while(true){
        lifeB -= atkA;
        if (lifeB <= 0) {
            console.log( "Yes" );
            return;
        }
        lifeA -= AtkB;
        if (lifeA <= 0){
            console.log( "No" );
            return;
        }
    }
});