remove N and W labels from map tick marks

I'm making a map in ggplot, and because I'm using the rnaturalearth package for the world basemap, the tick mark labels have N and W in them.

How do I remove the square box and the N or W symbols in the tick marks? The longitude values should be -0 to -70.

library(tidyverse)
library(rnaturalearth)
world <- ne_countries(scale = "medium", returnclass = "sf")
ggplot() +
  # basemap
  geom_sf(data = world, colour = NA, fill = "grey75") +
  coord_sf(ylim = c(43, 72), xlim = c(-68, -2)) +
  labs(x = "", y = "") +
  theme_bw()

You could set your desired format for the axes labels via the labels argument of scale_x/y_continuous, e.g. to achieve your desired result use labels = ~ .x:

library(tidyverse)
library(rnaturalearth)

world <- ne_countries(scale = "medium", returnclass = "sf")

ggplot() +
  geom_sf(data = world, colour = NA, fill = "grey75") +
  coord_sf(ylim = c(43, 72), xlim = c(-68, -2)) +
  labs(x = NULL, y = NULL) +
  scale_x_continuous(labels = ~ .x) +
  scale_y_continuous(labels = ~ .x) +
  theme_bw()