#include<cstdio>
#include <stdio.h>

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int i,j,prim[1000000],n,c=0;
    scanf("%d",&n);

    for(i=2;i<=n;i++)
        prim[i]=1;

    for(i=2;i<=n;i++)
        if(prim[i])
        {
            c++;
            for(j=i+i;j<=n;j+=i)
                prim[j]=0;
        }

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

    return 0;
}