#include <stdio.h>

int n, k;
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])
        {
            ++k;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
    printf("%d", k);
    return 0;
}