#include<fstream>

#define M 2000001

using namespace std;

FILE *f, *g;

int main()
{
    long i, j, n, cont=0;
    char p[M];

    f=fopen("ciur.in", "r");
    g=fopen("ciur.out", "w");

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

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

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

            for(j=i*i; j<=n; j+=i)
                p[j]=0;
            }

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

    fclose(f);
    fclose(g);

    return 0;
}