#include <bits/stdc++.h>
using namespace std;
int n, cnt;
char prim[2000005];
int main(void)
{
    int i, j;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &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;
        }
    printf("%d", cnt);
    return 0;
}