#include <stdio.h>

using namespace std;
int v[2000002];
FILE *f,*g;
int main()
{
    int n,i,j,nr=0;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    for(i=2;i<=n;i++)
    {
       if(v[i]!=1)
       {
           nr++;
           for(j=2*i;j<=n;j=j=j+i)
           {
               v[j]=1;
           }
       }
    }

    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;
}