[bzoj1968][Ahoi2005]COMMON 约数研究

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n<=1000000

这个嘛  直接枚举因数就好啦。

#include<iostream>
#include<cstdio>
#define MN 1000000
#define ll long long
using namespace std;
inline int read()
{
    int x = 0 , f = 1; char ch = getchar();
    while(ch < '0' || ch > '9'){ if(ch == '-') f = -1;  ch = getchar();}
    while(ch >= '0' && ch <= '9'){x = x * 10 + ch - '0';ch = getchar();}
    return x * f;
}

int n;
ll ans=0;

int main()
{
    n=read();
    for(int i=1;i<=n;i++)
        ans+=n/i;
    printf("%lld\n",ans);
    return 0;
}