#include <iostream>
#include <fstream>
using namespace std;
int N,cnt;
char prim[2000005];

int main(){
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int i,j;
    fin>>N;
    for(i=2;i<=N;++i)
        prim[i]=1;
    for(i=2;i<=N;++i)
        if(prim[i])
        {
            ++cnt;
            for(j=i+i;j<=N;j+=i)
                prim[j]=0;
        }
    fout<<cnt;

    return 0;
}