#include <cstdio>
FILE *g,*z;
using namespace std;
int main()
{
    z=fopen("ciur.out","w");
    g=fopen("ciur.in","r");
    int i,n,j,ct=0,v[19999999];
    fscanf(g,"%d",&n);
    fclose(g);
    for(i=2;i<=n;i++)
    v[i]=1;
    for(i=2;i<=n;i++)
    {
        if(v[i])
        {
            ct++;
            for(j=i+i;j<=n;j+=i)
            v[j]=0;
        }
    }
    fprintf(z,"%d",ct);
    fclose(z);
    return 0;
}