#include <cstdio>
#include <vector>

template <typename T> T read();
template <typename T> void write(T, char);
template <typename T> T max(T, T);
int find(int);
void merge(int, int);

const int MAXN = 1e5 + 10;

bool vis[MAXN];
::std::vector<int> primes;
void work(int n) {
  for (int i = 2; i <= n; ++i) {
    if (!vis[i]) {
      primes.push_back(i);
    }
    for (auto p : primes) {
      if ((long long) i * p > n) break;
      vis[i * p] = true;
      if (i % p == 0) break;
    }
  }
}

int a, b, p;
int num[MAXN];
int fa[MAXN];
int ans;
::std::vector<int> cache;

int main() {
  freopen("setb.in", "r", stdin);
  freopen("setb.out", "w", stdout);
  a = read<int>(), b = read<int>(), p = read<int>();
  work(b);
  while (primes.front() < p) primes.erase(primes.begin());
  for (int i = a; i <= b; ++i) {
    fa[i] = i;
  }

  while (true) {
    int cnt = 0;
    for (auto p : primes) {
      cache.clear();
      for (int i = max(::p, a); i <= b; ++i) {
        if (i % p == 0) {
          cache.push_back(i);
        }
      }

      for (int i = 0; i < (int) cache.size() - 1; ++i) {
        if (find(cache[i]) == find(cache[i + 1])) continue;
        cnt++;
        merge(cache[i], cache[i + 1]);
      }
    }

    if (!cnt) break;
  }

  for (int i = a; i <= b; ++i) {
    int fa = find(i);
    ans += (num[fa] == 0);
    num[fa] = 1;
  }

  write(ans, '\n');
  return 0;
}

int find(int x) {
  if (x == fa[x]) return x;
  return fa[x] = find(fa[x]);
}

void merge(int x, int y) {
  fa[find(y)] = find(x);
}

template <typename T> T max(T x, T y) {
  return x > y ? x : y;
}

#define isdigit(ch) (ch >= '0' && ch <= '9')
template <typename T> T read() {
  T res = 0, f = 1;
  char ch = getchar();
  for (; !isdigit(ch); ch = getchar())
    if (ch == '-') f = -1;
  for (; isdigit(ch); ch = getchar()) res = (res << 3) + (res << 1) + (ch ^ 48);
  return res * f;
}

template <typename T> void write(T x, char ed) {
  if (x < 0) x = -x, putchar('-');
  static int sta[sizeof(T) << 2], top = 0;
  do {
    sta[++top] = x % 10;
    x /= 10;
  } while (x);
  while (top) {
    putchar(sta[top--] ^ 48);
  }
  putchar(ed);
}