#include <fstream>
using namespace std;
FILE * fin = fopen("ciur.in","r");
FILE * fout = fopen ("ciur.out", "w");

int n;
int ciur[2000000];

int main()
{
    int i, j, nr=0;
    
    fscanf(fin, "%d", &n);
    
    for (i=2; i<=n; i++)
        if (!ciur[i])
        {
            nr++;
            for (j=2*i; j<=n; j+=i)
                ciur[j]=1;
        }
    
    fprintf(fout, "%d\n", nr);
    
    fclose(fin);
    fclose(fout);
    return 0;
}