#include <stdio.h>
#include <stdlib.h>
FILE *in,*out;
int n,i,j,nr;
char c[2000001];
int main()
{
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");
    fscanf(in,"%d",&n);
    for(i=2;i<=n;i++)
    {
        if(c[i]==0)
        {
            for(j=i*i;j<=n;j=j+i)
            {
                c[j]=1;
            }
        }
    }
    for(i=2; i<=n; i++)
    {
        if(c[i]==0)
        {
            nr++;
        }
    }
    fprintf(out,"%d",nr);

    fclose(in);
    fclose(out);
    return 0;
}