#include <iostream>
#include <fstream>
using namespace std;
long long N,i,j,nr,cnt;
int prim[2000005];
bool ok=1;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int main()
{ fin>>N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i]!=0)
        {
            ++cnt;
            for (j = i+i; j <= N; j=j+i)
                prim[j] = 0;
        }
        fout<<cnt;
}