#include<fstream>
#include<cstdio>

#define M 2000005

using namespace std;

int main()
{
    long i, j, n, cont;
    char p[M];

    ifstream f("ciur.in");
    ofstream g("ciur.out");

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

    cont=0;

    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<<cont<<endl;//fprintf(g, "%d\n", cont);

    return 0;
}