#include <fstream>
#include <bitset>
int N,g;
std::bitset <2000001>p;
std::ifstream fin("ciur.in");
std::ofstream fout("ciur.out");
int main(){
    fin>>N;
    for(int i=4;i<=N;i+=2)
        p[i]=1;
    for(int i=3;i*i<=N;i+=2)
        if(!p[i])
            for(int j=i*i;j<=N;j+=(i<<1))
                p[j]=1;
    for(int i=2;i<=N;++i)
        g+=(!p[i]);
    fout<<g;
    return 0;
}