#include<stdio.h>
FILE *in,*out;
using namespace std;
int n,nr,i,j;
char prim[2000005];
int main()
{
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");

    fscanf(in,"%d",&n);
    for (i=2; i<=n; i++)
        prim[i]=1;
    for (i=2; i<=n; i++)
        if (prim[i])
        {
            nr++;
            for (j=i+i; j<=n; j+=i)
                prim[j]=0;
        }
    fprintf(out,"%d",nr);
    fclose(in);
    fclose(out);
    return 0;
}