#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define maxn 2000010

int N, sol;
int prim[maxn];

int main() {
    FILE *f1=fopen("ciur.in", "r"), *f2=fopen("ciur.out", "w");
    int i, j;

    fscanf(f1, "%d\n", &N);

    for(i=2; i<=N; i++) {
         if(!prim[i]) {
              sol ++;
              for(j=2*i; j<=N; j+=i) {
                   prim[j] = 1;
              }
         }
    }

    fprintf(f2, "%d\n", sol);
    fclose(f1); fclose(f2);
    return 0;
}