ll@n,i,j;
char d[n+1]{};
d[1]=2;
rep(i,2,n+1){
	if(d[i]==0){
		rep(j,i,n+1,i){
			d[j]=(d[j]|2)^1;
		}
		rep(j,i*i,n+1,i*i){
			d[j]=4;
		}
	}
}
wt(sum[i,1,n+1](d[i]==2?1:d[i]==3?-1:0));