#include<stdio.h>
int n,c,j;
bool ciur[2000000];
int i;
FILE *in,*out;
int main ()
{
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");
    fscanf(in,"%d",&n);
    for(i=1;i<=n;i++)
    ciur[i]=1;
    for(i=2;i<=n;i++)
        if(ciur[i]==1)
        {
            c++;
            for(j=i+i;j<=n;j=j+i)
                ciur[j]=0;
        }
    fprintf(out,"%d",c);
    fclose(in);
    fclose(out);
    return 0;
}