#include <stdio.h>
#include <bitset>

using namespace std;

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

bitset<2000010> v;

int main()
{
    int n,nr=0,d,i;
    fscanf(f,"%d",&n);
    for (d=2;d*d<=n;d++)
        for (i=2;i*d<=n;i++)
            v[i*d]=1;
    for (i=2;i<=n;i++)
        if (!v[i]) nr++;
    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;
}