#include <stdio.h>

char v[2000005];

int main(void)
{
    int n=0,c=0,i=0,j=0;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for (i=2; i<=n; ++i) v[i]=1;
    for (i=2; i<=n; ++i)
    if (v[i])
    {
        ++c;
        for (j=i+i; j<=n; j+=i) v[j]=0;
    }
    printf("%d\n", c);
    return 0;
}