#include <bits/stdc++.h>
int main() {
  int a, b, c, count = 0;
  scanf("%d %d", &a, &b);
  if (1 <= a && c <= 10000 && a <= b) {
    for (a; a < b; a++) {
      if (a % c == 1) {
        count += 1;
      }
    }
    printf("%d\n", count);
  }
  return 0;
}
