#include <fstream>

using namespace std;

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

int n,i,nr,j;
char c[2000001];
int main()
{
    fscanf(f,"%d",&n);
    for (i=2;i<=n;i++)
        if (c[i]==0)
        {
            nr++;
            for (j=i*i;j<=n;j+=i)
                c[j]=1;
        }
    fprintf(g,"%d",nr);
    return 0;
}