hdu 4704 Sum (费马小定理+快速幂)

//(2^n-1)%mod
//费马小定理：a^n ≡ a^(n%(m-1)) * a^(m-1)≡ a^(n%(m-1)) (mod m)
# include <stdio.h>
# include <algorithm>
# include <string.h>
# define mod 1000000007
using namespace std;
__int64 pow(__int64 n)
{
__int64 p=1,q=2;
while(n)
{
if(n%2)
{
p=p*q%mod;
}
n/=2;
q=q*q%mod;
}
return p;
}
char str[1000100];
int main()
{

__int64 i,n,len;
while(~scanf("%s",str))
{
len=strlen(str);
n=0;
for(i=0;i<len;i++)
{
n=(n*10+str[i]-'0')%(mod-1);
}
printf("%I64d\n",pow(n-1));
}
return 0;
}