#include <cstdio>

#define file_in "ciur.in"
#define file_out "ciur.out"

int N,i,j,ans;
char prim[2010010];


int main(){
	
	freopen(file_in,"r",stdin);
	freopen(file_out,"w",stdout);
	
	
	scanf("%d", &N);
	ans=0;
	for (i=2;i<=N;++i)
		 if (!prim[i]){
			 ans++;
			 for (j=i+i;j<=N;j+=i)
				  prim[j]=1;
		 }
		 
	printf("%d\n", ans);

	return 0;
	
}