```
public class Solution {
public int UniquePaths(int m, int n) {
int[,] num = new int[m, n];
num[0,0] = 1;
for (int i = 1; i < m; i++)
num[i, 0] = 1;
for (int j = 1; j < n; j++)
num[0, j] = 1;
for (int i = 1; i < m; i++)
for (int j = 1; j < n; j++)
num[i, j] = num[i - 1, j] + num[i, j - 1];
return num[m - 1,n - 1];
}
}
```