#include <bits/stdc++.h>

#define MAXN 2000001

using namespace std;

int n, rad, nr = 1;
bool ciur[MAXN];

int main()
{
        freopen("ciur.in", "r", stdin);
        freopen("ciur.out", "w", stdout);
        scanf("%d", &n); rad = (int)sqrt(n);
        for(int i = 3; i <= rad; i += 2)
                if(ciur[i] == false)
                        for(int j = i * i; j <= n; j += i) ciur[j] = true;
        for(int i = 3; i <= n; i += 2)
                if(ciur[i] == false) ++nr;
        printf("%d", nr);
        return 0;
}