#include <bits/stdc++.h>

using namespace std;
int n, i, j, sol;
bitset<2000005>a;
void ciur()
{
    sol++;
    for(i = 3; i * i <= n; i += 2)
        if(!a[i])
        {
            sol++;
            for(j = i * i; j <= n; j += 2 * i)
                a[j] = 1;
        }
    for(; i <= n; i += 2)
        if(!a[i])
            sol++;
}
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    ciur();
    printf("%d", sol);
    return 0;
}