#include <bits/stdc++.h>
#define N 2000000
using namespace std;
bool ciur[N];
void CreateCiur ()
{
    int i, j;
    ciur[0]=ciur[1]=1;
    for (i=4; i<=N; i+=2)
        ciur[i]=1;
    for (i=3; i*i<N; i+=2)
        if (ciur[i]==0)
            for (j=i*i; j<=N; j+=2*i)
                ciur[j]=1;
}
int main()
{
    CreateCiur();
    int cnt=0, n;
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin >> n;
    for (int i = 1; i<=n; i++)
        if (ciur[i]==0) cnt++;
    fout << cnt;
    return 0;
}