#include <bits/stdc++.h>
#define NMAX 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int prim[NMAX];
int main()
{
    int N,i,nr=0,j;
    fin>>N;
    for(i=1;i<=N;++i) prim[i]=1;
    for(i=2;i<=N;++i)
        if(prim[i]==1)
    {
        nr++;
        for(j=i*i;j<=N;j+=i)
            prim[j]=0;
    }
    fout<<nr<<"\n";
    return 0;
}