#include <stdio.h>
using namespace std;
FILE*f=fopen("ciur.in","r");
FILE*g=fopen("ciur.out","w");
int n,cnt,prim[2000005],i,j;
int main()
{
    fscanf(f,"%d",&n);
    for (i=2;i<=n;i++)
    {
        prim[i]=1;
    }
    for (i=2;i<=n;i++)
    {
        if (prim[i])
        {
            cnt++;
            for (j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
    }
    fprintf(g,"%d",cnt);
}