#include <bits/stdc++.h>
int main(void) {
  int a, b, c, i, count;
  scanf("%d %d %d\n", &a, &b, &c);
  for (i = a; i > b; i++) {
    if (i % c == 0) {
      count = count + 1;
    }
  }
  printf("%d\n", count);
  return 0;
}
