#include <stdio.h>
#include <math.h>

int long unsigned i,rK,vprim [100000] = {2};
int long unsigned  prim(int long unsigned  a,int long unsigned K)
{
	rK = (int long unsigned) sqrt(K);
	for(i=0;i<=rK;i++){	if(a%vprim[i] == 0){ return 0;}}
	vprim[i]=a;
	return 1;
}
 
int main(void)
{
	int long unsigned  i=1,N,K=1;
	freopen("ciur.in","r",stdin);
		scanf("%ld",&N);
	fclose(stdin);
	for(i=3;i<=N;i+=2)
	{
		if (prim(i,K)) K++;
	}
	freopen("ciur.out","w",stdout);
		printf("%ld",K);
	fclose(stdout);
	return 0;
}