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

#define maxn 2000033
using namespace std;

int N, prime_count;
bool prim[maxn];

void ciur()
{
	long long i=0,j=0;
	prime_count=1;
	for (i=3; i<=N; i+=2)
		if (!prim[i])
		{
			for (j=i; j*j<=N; j+=i)
				prim[j]=true;
			++prime_count;
		}
}



int main()
{
	FILE *fin = fopen("ciur.in", "rt"), *fout = fopen("ciur.out", "wt");
	fscanf(fin, "%d", &N);
	ciur();
	fprintf(fout, "%d", prime_count);
	return 0;
}