分块

LL fenkuai(LL k){
    LL j;
    LL ans=0;
    for (LL i=1;i<=k;i=j+1){
        j=n/(n/i);
        ans+=(j-i+1)%mod*((n/i)%mod)%mod;
        ans%=mod;
    }
    return ans;
}