#include <bits/stdc++.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool prim[2000001];
int contor = 0;
int main()
{
    int n,i,a,j;
    in>>n;
    for(i=2; i<=n; i++)
    {
        if(prim[i] == 0)
        {
            contor++;
            for(j=i*i; j<=n; j=j+i)
            {
                prim[j]=1;
            }
        }
    }
    out<<contor;
    return 0;
}