#include<fstream>
#include<cstdio>

#define M 2000005
using namespace std;

long i, j, n;
int cont;
char p[M];


ifstream f("ciur.in");
FILE *g;



int main()
{

    f>>n;//fscanf(f, "%d", &n);
    f.close();

    for(i=2; i<=n; i++)
        p[i]='1';

    for(i=2; i<=n; i++)
        if(p[i]=='1')
            {
            cont++;

            for(j=i*i; j<=n; j+=i)
                p[j]='0';
            }
    g=fopen("ciur.out", "w");
    fprintf(g, "%d\n", cont);
    return 0;
}