#include <fstream>

using namespace std;

const int DIM = 2000001;

bool c[DIM];
int n, nr;

int main() ,{
    FILE *f=fopen("ciur.in","r");
    FILE *g=fopen("ciur.out", "w");

    int i,j;

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

    for(i = 2; i <= n; ++i)
       if(!c[i])
            for (j = 2 * 1;j <= n ; j += i)
               c[j] = 1;

     for(i = 2; i <= n; ++i)
                if(!c[i])
                   ++nr;

     fprintf(g , "%d" , nr);

     fclose(f);
     fclose(g);

    return 0;
}