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