#include <cstdio>
#include <bitset>

#define NMAX 2000010

using namespace std;

bitset<NMAX> Ciur;

int Solve(int N)
{
    if(N<2)
        return 0;
    if(N==2)
        return 1;
    int c = 1;

    for(int i=3;i<N;i+=2)
    {
        if(Ciur[i])
            continue;
        c++;
        for(int j=i+i+i;j<N;j+=i+i)
            Ciur[j]=true;
    }

    return c;
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int N;
    scanf("%d",&N);
    int c = Solve(N);
    printf("%d\n",c);

    return 0;
}