#include<stdio.h>      
#define NMAX 2000010

int main(){

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

char vprim[NMAX+1]={1,1};
  
int i,j,n,nr=0;

scanf("%d\n",&n);

for(i=2;i<=n/2;i++){
		if(vprim[i]==0)
			for(j=2;j*i<=n;j++)
				vprim[j*i]=1;
}

for(i=1;i<=n;i++)
	if(vprim[i]==0) nr++;
printf("%d\n",nr);
return 0;
}