#include<stdio.h>

int nb;
int N;

bool notprimes[2000001];

int main(){
	
	FILE* f= fopen("ciur.in","rt");
	FILE* g= fopen("ciur.out","wt");
	
	fscanf(f,"%d",&N);

	for(int i=2;i<=N;i++){
		if(notprimes[i]==false){
			nb++;
			for(int j=2*i;j<=N;j+=i)
				notprimes[j]=true;
		}
	}

	fprintf(g,"%d",nb);
	
	fclose(g);
	fclose(f);
	return 0;
}