#include <bits/stdc++.h>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

bool ciur[2000005];

int main()
{
    int i,j,n,sol=1;
    f>>n;
    ciur[0]=ciur[1]=1;
    for(i=4;i<=n;i+=2)ciur[i]=1;

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