#include <iostream>
#include<algorithm>
using namespace std;
const int N=2000001;
bool c[N];
int main()
{
    int n,i,j,nr=0;
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
    for(i=2;i*i<N;i++)
        if(not c[i])
            for(j=i*i;j<N;j+=i)
                c[j]=true;
    nr=0;
    for(i=2;i<=n;i++)
        if(not c[i])
            nr++;
    out<<nr;
    in.close();
    out.close();
    return 0;
}