#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
const int MAX=2000001;
char v[MAX];
int n;
int radical(int x){
    double y;
    y=x/2;
    while((int)y*(int)y>x || (int)(y+1)*(int)(y+1)<=x){
        y=(y+x/y)/2;
    }
    return (int)y;
}
int ciur()
{
    int ans=1,i,rad=radical(n);
    for(i=3;i<=rad;i=i+2)
        if(v[i]==0){
            for(int j=i*i;j<=n;j=j+i+i)
                v[j]=1;
            ans++;
        }
    for(;i<=n;i=i+2)
        if(v[i]==0) ans++;
    return ans;
}
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    g<<ciur();
    return 0;
}