#include <stdio.h>
#include<string.h>

char p[2000001];

int primes(int n){
	int i,j, count = 0;
	
	for(i = 2; i <= n; ++i){
		if(p[i] == 0){ 
			count++;
			for(j = 2 * i; j <= n; j += i){
				p[j] = 1;
			}
		}
	}
	return count;
}


int main(){
	
	FILE *fi = fopen("ciur.in","r");
	FILE *fo = fopen("ciur.out","w");
	
	int n;
	
	fscanf(fi,"%d",&n);
	
	fprintf(fo, "%d", primes(n));
	
	return 0;
	
}