#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n,i,nr=1,j;
    char *a;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    a=calloc(2000002,sizeof(char));
    for(i=3; i<=n; i+=2)
    {
        if(a[i]==0)
        {
            nr++;
            for(j=i; j<=n; j+=i)
                a[j]=1;
        }
    }
    printf("%d\n",nr);
    free(a);
    return 0;
}