#include <stdio.h>
#include <vector>

using namespace std;

vector < bool > ciur (2002000);

int main(){
    
    int nr=0,n;
    
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    scanf("%d",&n);
    
    for (int i=2;i<=n;++i)
	if(!ciur[i])
	    for(int j=i+i;j<=n;j+=i)
		ciur[j]=1;
    
    for (int i=2;i<=n;++i)
	if(!ciur[i])
	    ++nr;
    
    printf("%d\n",nr);
    
    return 0;
}