题解 | #【模板】整除分块#

#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    long long n; 
    if (!(cin >> n)) return 0;
    long long ans = 0;
    for (long long i = 1; i <= n; ) {
        long long q = n / i;
        long long r = n / q; // 最大 i 使得 floor(n/i)=q
        ans += (r - i + 1) * q;
        i = r + 1;
    }
    cout << ans << '\n';
    return 0;
}

import java.io.*;

public class Main {
    static class FastScanner {
        private final InputStream in;
        private final byte[] buffer = new byte[1 << 16];
        private int ptr = 0, len = 0;
        FastScanner(InputStream is) { this.in = is; }
        private int read() throws IOException {
            if (ptr >= len) { len = in.read(buffer); ptr = 0; if (len <= 0) return -1; }
            return buffer[ptr++];
        }
        long nextLong() throws IOException {
            int c; long sgn = 1, x = 0;
            do { c = read(); } while (c <= 32);
            if (c == '-') { sgn = -1; c = read(); }
            while (c > 32) { x = x * 10 + (c - '0'); c = read(); }
            return x * sgn;
        }
    }

    public static void main(String[] args) throws Exception {
        FastScanner fs = new FastScanner(System.in);
        long n = fs.nextLong();
        long ans = 0;
        for (long i = 1; i <= n; ) {
            long q = n / i;
            long r = n / q;
            ans += (r - i + 1) * q;
            i = r + 1;
        }
        System.out.println(ans);
    }
}

import sys

data = sys.stdin.buffer.read().split()
n = int(data[0])
ans = 0
i = 1
while i <= n:
    q = n // i
    r = n // q
    ans += (r - i + 1) * q
    i = r + 1
print(ans)