#include<cstdio>
using namespace std;
int a[2000001];
int main ()
{
    int n,i,nr=0,j;
    FILE *f,*g;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);

   for(i=2;i*i<=n;i++)
        if(a[i]==0)


        for(j=2;j*i<=n;j++)
            a[i*j]=1;

             for(i=2;i<=n;i++)
                if(a[i]==0)
                nr++;

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

    return 0;

}