#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int N, cnt;
char prim[2000005];
int main(void)
 {
int i, j;
 f>>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;
        }
g<<cnt;
return 1;
}