/******************************************************************************

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*******************************************************************************/
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N,k;
bool a[2000002];
int main()
{
    f >> N;
    k = 1;
    
    for(int i = 4; i <= N; i+=2){
        a[i] = 1;
    }
    for(int i = 3; i <= N; i+=2){
        if(a[i] == 0){
            k++; 
        for(int j = i+i; j <= N; j+=i){
            a[j] = 1;
         }
        }
    }
    g << k;
    return 0;
}