#include <stdio.h>
#include <stdlib.h>
int n,nrp;
char prim[2000005];
int main()
{
    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])
        {
            ++nrp;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
    printf("%d\n", nrp);
    return 0;
}