#include<cstdio>
using namespace std;

int i,j,n,nr;
bool a[2016401]={0};



int main(){
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

	scanf ("%d", &n);
	nr=0;
	for (i=2; i<=n; i++){
		if (a[i]==0){
			nr++;
			if (i<=1420){
				for (j=i*i; j<=2016400; j=j+i){
					a[j]=1;
				}
			}
		}
	}
		
	printf ("%d", nr);
	return 0;
}