#include
#include
using namespace std;
int main()
{
int n=0,fuhao=-1;
double x=0,jc=1,fx=1,sum=1;
cout << "input n: " ;
cin >> n ;
cout << "input x: " ;
cin >> x ;
for( int i=1;i<=n;i++ )
{
jc *= i ;
fx *= x ;
sum += fuhao*fx/jc ;
fuhao=-fuhao;
}
cout<< sum << endl;
return 0;
}