#include <stdio.h>

const int v_LIMIT = 2000000;
bool v[v_LIMIT];
int c = 0, n;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);

    for(size_t i = 2; i * i <= n; i++)
        if(v[i] == false)
            for(size_t k = i; k <= i * i; k += i)
                v[k] = true;
    for(size_t i = 2; i <= n; i++)
        if(v[i] == false)
            c++;
    printf("%d", c);

    return 0;
}