#include <bits/stdc++.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
const int N=2000010;
char p[N];
int n,sol;

int main()
{
    f>>n;
    if(n>=2)
        sol++;
    int i;
    for(i=3;i*i<=n;i+=2)
        if(!p[i])
        {
            sol++;
            for(int j=i*i;j<=n;j+=i*2)
                p[j]=1;
        }
    for(;i<=n;i+=2)
        if(!p[i])
            sol++;
    g<<sol;
    return 0;
}