int main(void) {
    int A, B, C, D;
    scanf("%d", &A);
    scanf("%d", &B);
    scanf("%d", &C);
    scanf("%d", &D);

    while(1){
        C = C - B;
        if(C<=0){
            printf("Yes");
            break;
        }
        A = A - D;
        if(A<=0){
            printf("No");
            break;
        }
    }
}