# Polygon - Is-Convex

Time Limit : 1 sec, Memory Limit : 131072 KB
Japanese version is here

# Is-Convex

For a given polygon g, print "1" if g is a convex polygon, "0" otherwise. Here, in a convex polygon, all interior angles are less than or equal to 180 degrees.

g is represented by a sequence of points p1, p2,..., pn where line segments connecting pi and pi+1 (1 ≤ in-1) are sides of the polygon. The line segment connecting pn and p1 is also a side of the polygon.

## Input

g is given by coordinates of the points p1,..., pn in the following format:

```n
x1 y1
x2 y2
:
xn yn
```

The first integer n is the number of points. The coordinate of a point pi is given by two integers xi and yi. The coordinates of points are given in the order of counter-clockwise visit of them.

## Output

Print "1" or "0" in a line.

## Constraints

• 3 ≤ n ≤ 100
• -10000 ≤ xi, yi ≤ 10000
• No point of the polygon will occur more than once.
• Two sides of the polygon can intersect only at a common endpoint.

```4
0 0
3 1
2 3
0 3
```

```1
```

```5
0 0
2 0
1 1
2 2
0 2
```

```0
```