Sum HDU - 4704

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <cstdio>
#include <bitset>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <set>

#define FOR(i,a,b) for(int i=a;i<=b;i++)
#define ROF(i,a,b) for(int i=a;i>=b;i--)
#define mem(i,a) memset(i,a,sizeof(i))
#define rson mid+1,r,rt<<1|1
#define lson l,mid,rt<<1

#define mp make_pair
#define pb push_back
#define ll long long
#define LL long long
using namespace std;
template <typename T>inline void read(T &_x_){
_x_=0;bool f=false;char ch=getchar();
while (ch<'0'||ch>'9') {if (ch=='-') f=!f;ch=getchar();}
while ('0'<=ch&&ch<='9') {_x_=_x_*10+ch-'0';ch=getchar();}
if(f) _x_=-_x_;
}
const double eps = 1e-8;
const int maxn = 2e5+7;
const int mod = 1e9+7;
const ll inf = 1e15;

char s[maxn];

ll fast_mod(ll n){
ll bs=2,ans=1;
while(n){
if(n&1) ans=ans%mod*bs%mod;
bs=(bs*bs)%mod;
n>>=1;
ans%=mod;
}
return ans%mod;
}

int main(){
while(~scanf("%s",s+1)){
int len =strlen(s+1);
ll md = 0;
FOR(i,1,len){
md+=(s[i]-'0');
if(i!=len) md*=10;
md%=(mod-1);
}
md-=1;             //之前这一句写的是if（md==0） md=mod-1,然后下面这一句写的是md-=1;然后wa了。。。难道经过上面的运算md还能小于0么....又没有减法。。。。
md=(md+mod)%mod;
printf("%I64d\n",fast_mod(md));
}
return 0;
}