function main(input) {
    input = input.trim().split(" ").map(x => Number(x));
    while (true) {
        input[2] -= input[1];
        if (input[2] <= 0) {
            console.log("Yes");
            break;
        }
        input[0] -= input[3];
        if (input[0] <= 0) {
            console.log("No");
            break;
        }
        
    }
}

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