#include <fstream>
#define MAX 2000005
#define RMAX 1415
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n,ans;
bool B[MAX];

void ciur(){
    int i,j;
    if(n>=2)++ans;
    for(i=3;i<RMAX;i+=2){
        if(!B[i]){
            if(i<=n)
                ++ans;
            else
                return;
            for(j=i*i;j<MAX;j+=i)
                B[j]=1;
        }
    }
    for(i=RMAX;i<MAX;++i){
        if(!B[i]){
            if(i<=n)
                ++ans;
            else
                return;
        }
    }
}

int main(){
    fin>>n;
    ciur();
    fout<<ans;
    return 0;
}