#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

int fa[100010], a, b, p, ans;
bool is_prime[100010];
int find(int x) { return fa[x] == x ? x : fa[x] = find(fa[x]);}
void prepare() {
	scanf("%d %d %d", &a, &b, &p);
	for (register int i = a; i <= b; i ++)
		fa[i] = i;
}

void solve() {
	ans = b - a + 1;
	for (register int i = 2; i <= b; i ++) {
		if (!is_prime[i]) {
			if (i >= p)
				for (register int j = i * 2; j <= b; j += i) {
					is_prime[j] = true;
					if (j - i >= a && find(j) != find(j - i))
						fa[find(j)] = find(j - i), ans --;
				}
			else for (register int j = i * 2; j <= b; j += i)
				is_prime[j] = true;
		}
	}
	printf("%d\n", ans);
}

int main() {
	freopen("setb.in", "r", stdin);
	freopen("setb.out", "w", stdout);
	prepare();
	solve();
	return 0;
}