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if __name__ == "__main__":
    n: str = input()
    text: str = input()

    tests = int(int(n) / 10)
    result = 0
    passed = 0
    for i, char in enumerate(text):
        if char == "T":
            passed += 1
        if ((i + 1) % tests) == 0:
            result += int(passed / tests)
            passed = 0


    print(result)