#include <stdio.h>
#include <math.h>

#define MX 2000001

using namespace std;

long n,i,j,nr;
char ciur[MX];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    ciur[1]=ciur[0]=1;
    for(i=2;i*i<=MX;i++)
    if(!ciur[i])
    for(j=2;j*i<=MX;j++)
    ciur[i*j]=1;
    for(i=2;i<=n;i++)
	if(!ciur[i])
	nr++;
    printf("%ld",nr);
    return 0;
}