#include <cstdio>
#define LMAX 2000000
using namespace std;
bool ciur[LMAX+5];
inline void CIUR(){
	int d,i;
	for(i=4;i<=LMAX;i+=2)
		ciur[i]=1;
	for(d=3;d*d<=LMAX;d+=2)
		if(!ciur[d])
			for(i=d*d;i<=LMAX;i+=2*d)
				ciur[i]=1;
}
int main(){
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	CIUR();
	int n,i,ap=0;
	scanf("%d",&n);
	for(i=2;i<=n;++i)
		if(!ciur[i])
			ap++;
	printf("%d\n",ap);
	fclose(stdin),fclose(stdout);
    return 0;
}