#include <stdio.h>   
long n,i,j,q;   
char prim[2000001];   
int main(){   
    freopen("ciur.in","r",stdin);   
    freopen("ciur.out","w",stdout);   
    scanf("%ld",&n);   
    q=1;   
    for (i=3;i<=n;i+=2)   
        if (!prim[i]){   
            q++;   
            for (j=3*i;j<=n;j+=2*i)   
                prim[j]=1;   
        }   
    printf("%ld\n",q);   
return 0;   
}