#include <stdio.h>
int N,ct;
char prim[2000005];

int main(void)
{
    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]){
            ct++;
            for(j=i+i;j<=N;j+=i){
                prim[j]=0;
            }
        }
    }
    printf("%d\n",ct);
    return 0;
}