#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int erath[2000005];
int main()
{
    int n,s;
    fin>>n;
    s=0;
    erath[0]=1;
    erath[1]=1;
    for(int div=2;div*div<=n;div++){
        if(erath[div]==1){
            continue;
        }
        for(int mul=2*div;mul<=n;mul+=div){
            erath[mul]=1;
        }
    }
    for(int i=0;i<=n;i++){
        if(erath[i]==0){
            s++;
        }
    }
    fout<<s;
    return 0;
}