#include <bits/stdc++.h>
#include <cstring>
# define pb push_back
#define nmax 100002
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
string a,b;
int n,k,i,d;
bool ciur[2000004];

int main()
{
    f>>n;
    for(d=2;d*d<=n;d++)
    if(ciur[d]==0)
        for(i=d*d;i<=n;i+=d)
        ciur[i]=1;

    for(i=2;i<=n;i++)
        if(!ciur[i])
        k++;
    g<<k;
    return 0;
}