Code:

if __name__ == "__main__":
    s = v = 0
    step = int(input())
    str = input()

    for idx,val in enumerate(str):
        if val == "D":
            s = s-1
        if val == "U":
            s = s+1
        if idx > 0 and s == 0 and val == 'U':
            v = v+1
    print(v)

Test Case:

8
UDDDUDUU

Result:

1

Run:

Ideone.com