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