#include <cstdio>
#include <vector>
using namespace std;

vector <char> a;

int main()
{
    int n,i,nc=2,np=0;
    FILE *f=fopen("ciur.in","r");
    fscanf(f,"%d",&n);
    fclose(f);
    for(i=1;i<=n;i++)a.push_back(0);
    while(1)
    {
        while(nc<=n && a[nc])nc++;
        if(nc>n)break;
        i=2;
        while(nc*i<=n)a[(i++)*nc]=1;
        nc++;np++;
    }
    f=fopen("ciur.out","w");
    fprintf(f,"%d",np);
    return 0;
}