using R - delete rows when a value repeated less than 3 times

frame with 10 rows and 3 columns

    a   b c
1   1 201 1
2   2 202 1
3   3 203 1
4   4 204 1
5   5 205 4
6   6 206 5
7   7 207 4
8   8 208 4
9   9 209 8
10 10 210 5

I want to delete all rows where the same value in the column "c" repeated less than 3 times. In this example I want to remove rows 6, 9 and 10. (my real data.frame has 5000 rows and 25 cols) I tried to do it using the function rle, but I keep getting the wrong solution. any help? thanks!