#include <bits/stdc++.h>
using namespace std;

int n;
bool p[2000005];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    int NR = 1;
    for(int i = 3; i * i <= n ; i += 2){
        if(p[i] == 0){
            for(int j = i * i ; j <= n ; j += (i << 1))
                p[j] = 1;
        }
    }
    for(int i = 3; i <= n ; i += 2)
        if(p[i] == 0) ++NR;
    printf("%d", NR);
    return 0;
}