#include <stdio.h>
#include <string.h>
#include <math.h>

char sev[2000005];
int n, sol;

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

    scanf("%d", &n);
    int i, j;

    memset(sev, 1, n+1);

    for(i = 2; i <=n; i++)//i <= n; pentru a se calcula toate sol
        if(sev[i])
        {
            sol++;
            for(j = i*2; j<=n; j+=i)
                sev[j] = 0;
        }

    printf("%d\n", sol);

    return 0;
}