#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long long contor,i,j;
int main()
{
    bool x[2000001];
    int n;
    fin>>n;
    for(i=1; i<=n; ++i)
    {
        x[i]=1;
    }
    for(i=2;i<=n;++i)
    {
        if(x[i]==1)
        {
            contor+=1;
            for(j=i*i;j<=n;j=j+i)
            {
                x[j]=0;
            }
        }
    }
    fout<<contor;
    return 0;
}