#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool pr[2000001];
int main()
{
    int n,i,j,cnt;
    fin>>n;
    pr[0]=pr[1]=1;
    for(i=4;i<=n;i+=2)
        pr[i]=1;
    for(i=3;i*i<=n;i+=2)
        if(pr[i]==0)
            for(j=i*i;j<=n;j+=i)
                pr[j]=1;
    if(n<2)
        cnt=0;
    else
    {
        cnt=1;
        for(i=3;i<=n;i+=2)
            if(pr[i]==0)
                ++cnt;
    }
    fout<<cnt;
}