#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int i,n,j,nr=0;
char prim[2000001];
int main()
{   f>>n;
    for(i=2;i<=n;i++)prim[i]=1;
    for(i=2;i<=n/2;i++)if(prim[i]==1)
        for(j=2;j<=n/i;j++)prim[i*j]=0;
    for(i=2;i<=n;i++)
        if(prim[i]==1)nr++;
        g<<nr;
}