#include<stdio.h>   
long sol[1024],cnt,n,m;   
char prim[2000005];   
int main()   
    {   
    long i,j;cnt=0;m=0;   
    FILE*f,*g;   
    f=fopen("ciur.in","r");   
    g=fopen("ciur.out","w");   
    fscanf(f,"%ld",&n);   
    for(i=2;i<=n;i++)   
        prim[i]='1';   
    for(i=2;i<=n;i++)   
        if(prim[i]=='1')   
            {   
            m++;   
            for(j=i+i;j<=n;j+=i)   
                prim[j]='0';   
            }   
    fprintf(g,"%ld\n",m);   
    
    fcloseall();   
    return 0;   
        }