Ural 1020 Rope

Ural 1020 Rope

Nothing to say.
Here is my code：

#include < stdio.h >
#include < math.h >
#define  maxn 107
#define  pi acos(-0.1)
int  main()
{
     /*
    freopen("data.in","r",stdin);
    freopen("data.out","w",stdout);
    // */
     long  n;
     double  r,ans,x[maxn],y[maxn];
    scanf( " %ld%lf " , & n, & r);
    ans = 2 * acos( - 1.0 ) * r;
     for ( long  i = 1 ;i <= n;i ++ )
        scanf( " %lf%lf " , & x[i], & y[i]);
     for ( long  i = 2 ;i <= n;i ++ )
        ans += sqrt((x[i] - x[i - 1 ]) * (x[i] - x[i - 1 ]) + (y[i] - y[i - 1 ]) * (y[i] - y[i - 1 ]));
    ans += sqrt((x[n] - x[ 1 ]) * (x[n] - x[ 1 ]) + (y[n] - y[ 1 ]) * (y[n] - y[ 1 ]));
    printf( " %.2lf\n " ,ans);
return   0 ;
}