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